US3714644A - Alarms for night latch - Google Patents

Alarms for night latch Download PDF

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US3714644A
US3714644A US3714644DA US3714644A US 3714644 A US3714644 A US 3714644A US 3714644D A US3714644D A US 3714644DA US 3714644 A US3714644 A US 3714644A
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means
alarm
circuit
keeper
member
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H Hellstrom
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H Hellstrom
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    • EFIXED CONSTRUCTIONS
    • E05LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
    • E05BLOCKS; ACCESSORIES THEREFOR; HANDCUFFS
    • E05B45/00Alarm locks
    • E05B45/005Chain-locks, cable-locks or padlocks with alarms
    • EFIXED CONSTRUCTIONS
    • E05LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
    • E05CBOLTS OR FASTENING DEVICES FOR WINGS, SPECIALLY FOR DOORS OR WINDOWS
    • E05C17/00Devices for holding wings open; Devices for limiting opening of wings or for holding wings open by a movable member extending between frame and wing; Braking devices, stops or buffers, combined therewith
    • E05C17/02Devices for holding wings open; Devices for limiting opening of wings or for holding wings open by a movable member extending between frame and wing; Braking devices, stops or buffers, combined therewith by mechanical means
    • E05C17/04Devices for holding wings open; Devices for limiting opening of wings or for holding wings open by a movable member extending between frame and wing; Braking devices, stops or buffers, combined therewith by mechanical means with a movable bar or equivalent member extending between frame and wing
    • E05C17/36Devices for holding wings open; Devices for limiting opening of wings or for holding wings open by a movable member extending between frame and wing; Braking devices, stops or buffers, combined therewith by mechanical means with a movable bar or equivalent member extending between frame and wing comprising a flexible member, e.g. chains
    • E05C17/365Security chains
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T292/00Closure fasteners
    • Y10T292/28Extension link
    • Y10T292/283Chain

Abstract

An alarm system includes a latch mechanism having a flexible connective member with one end anchored for example to a wall or door frame and the other end detachably securable to the door. Sensory means are extended along at least a portion of the flexible member, and circuit means are coupled to the sensory means for energizing an alarm mechanism upon occurrence of a malfunction in the sensory means.

Description

United States Patent Hellstrom 1 Jan. 30, 1973 541 ALARMS FOR NIGHT LATCH 2,686,909 8/1954 POUlSOn ..340 2 56 x 1 Q 1 3,014,207 12/1961 Principale ..340/256 x Hamld REM"! l' 5245 3,295,123 12 1966 Winterringer... ..340 274 Center Avenue, Pmsburgh, 521,239 6/1894 Hoopes ..340/274 15232 3,444,546 5/1969 Hawkins ..340/274 [221 Filed: FOREIGN PATENTS OR APPLICATIONS 1 1 PP 92,673 621,453 3/1927 France ..340/274 Priniary ExaminerJohn W. Caldwell [52] U.S. Cl ..340/274, ZOO/61.62 511 1111.01. ..G08b 13/08, G081) 13/12 Assistant Examiner-scofl Partridge [58] Field 61 Search ..340/274, 276, 280, 380, 256, W-

340/273; ZOO/61.62, 61.81, 61.93, 61.08;

174/34, 36 [57] ABSTRACT An alarm system includes a latch mechanism havinga References Cited flexible connective member with one end anchored for example to a wall or door frame and the other end UNITED STATES PATENTS detachably securable to the door. Sensory means are 1,732,276 10 1929 Morrison ..340/256 ded al ng at l ast a p rtion of the flexible 3,553,721 1/1971 Hawkins ..340/276 X member, and circuit means are coupled to the sensory 3,594,770 7/1971 Ham et a1. ..340/273 means for energizing an alarm mechanism upon oc- 2,943,308 6/1960 wCSIphal ..340/276 currence of a malfunction'in the ensory means 3,588,811 6/1971 Prickett ..340/3 80 3,440,636 4/1969 Sliman ..340/280 20 Claims, 13 Drawing Figures 67 76 llllll M l i1 I I 22 f 82 \J a 9 PAIENTEuJmman 3,714,644

sum 1m 3 F IG].

mvsmfim HAROLD RICHARD HELLSIROM PATENTEUJAI 30 I973 SHEET 2 0F 3 46'GUARD WIRES l I l I IZ'CIONTINUITY LOOP ALARM INVENTOR. HAROLD RICHARD HELLSTROM FIG. 6

HIS A ORNE I PATENTEDJAN so 1915 3,714,644 SHEET 30F 3 L s52 98 96 EH02 FIGAA INVENTOR.

HAROLD RICHARD HELLST ROM HIS TORNEY v ALARMS FOR NIGHT LATCH The present invention relates to burglar or tampering alarm devices and more particularly to a device of the character described incorporated in a night latch using a flexible connective member such as a chain. The alarm is arranged to indicate breakage of or tampering with the night latch connective member or associated components such asthe anchor and keeper plates.

A chain type night latch is widely used on entrance doors to private and multiple dwellings, multiple unit apartments, offices and office suites and the like. in the usual forms of this type of night latch, a short length of chain is usually affixed to the door frame or the wall adjacent thereto. The free end of the chain terminates in a keeper which can be keyed into an elongated slot in a keeper plate usually attached to the door. The arrangement of parts can be and frequently is reversed. In the usual configuration the remote end of the slot is enlarged such that a keying portion of the chain keeper can be inserted therethrough where upon the keeper is retained in the slot as it moves therealong toward the adjacent edge of the entrance door. In most cases the chain is only of sufficient length to permit insertion of its keeper into the remote end of the keeper plate slot when the door is completely closed. When the entrance door is set slightly ajar the keeper is moved to the nearer end of the keeper plate slot to afford a narrow opening of not more than an inch or two. This affords the occupant of the dwelling, office or other space visual access to ascertain the identity of any caller or visitor or to receive small articles through the visual access opening such as letters, newspapers, prescriptions and the like without fully unlatching the door and subjecting the premises to the possibility of forceful, violent, or other unwanted entrance.

The chain type night latch or lock also secures the entrance to the dwelling or other space protected thereby against the possibility of an occupants having lost his key, which may have been found by an adverse or other undesirable person. Use of a chain lock or some other form of night latch is a double check against an occu'pants forgetting to set the night latch usually forming part of a conventional key lock customarily used for'entrance doors.

Notwithstanding the inspectional aspects of the use of a chain type latch, there are certain disadvantages inherent in such use. For example if an intruder or other adverse party'possesses a key to the house or apartment or other dwelling whose entrance door is protected by a chain type night latch, frequently the entrance door can be opened, after the intruder unlocks the usual entrance key lock, sufficiently to permit insertion of a wire or other object for the purpose of removing the chain keeper from the remote end of the keeper plate slot. By this means, a burglar or other intruder can gain entrance tothe premises without arousing the sleeping occupants. in any event the entrance door can be opened sufficiently (taking advantage of the aforementioned visual access) to permit a burglar, robber, or other intruder to insert a tool or weapon for the purpose of breaking the chain latch or otherwise dislodging components thereof or in some cases to permit a direct attack upon the occupant or occupants of the premises. For example, an intruder may knock at the entrance door in the ordinary manner, whereupon the occupant opens the entrance door but only to the extent permitted by the chain latch to ascertain who the expected or unexpected caller might be. The intruder or attacker may then swing a tire iron or other weapon through the visual access opening permitted by the chain lock for the purpose either of attacking the occupant if he or she remains within reach or for striking and severing the chain to gain access to the premises.

With the exponential increases in criminal activities, apparently engendered by the modern enlightenment of our latterday civilization, the incorporation of an alarm system in conjunction with a conventional and widely used chain type or similar night latch becomes increasingly undesirable. Such alarm system can be arranged to sound an internal alarm, i.e. an alarm only within the premises, for the purpose of awakening sleeping occupants to the activities of a burglar or other sneak thief. Alternatively the alarm system can be arranged to sound an external alarm, for example in the building managers office or apartment, house detectives office, or the like in the case of an apartment house or other multiple dwelling, or an alarm in a nearby police or fire station. The latter alarm system would of course be more advantageous in the case of attempted entrance by robbers or burglars attempting to gain access by violence either against the occupant or by mutilating the chain latch through the visual access opening afforded thereby. An ultimate in protection can be afforded by use of a combination of these systems.

1 am aware of course of the efforts of others in this and related fields. The US. Pats. to Chick et al No. 3,340,522 and to Hawkins No. 3,406,386, and British Patent No. 636,985 each relate to an alarm device in conjunction with a night latch such as a chain lock. in every case, however, the alarm device is unable to distinguish between an inadvertant opening of the door (to the extent permitted by the chain or other flexible member) and an actual breaking or attempt at breaking the chain. Moreover the aforementioned alarm systems and also the differently-actuated alarm system disclosed in U.S. Pat. to Fruh No. 2,607,866 depends upon a mechanical switch actuation, i.e. the pulling of some flexible or essentially flexible member, to operate the alarm.

The US. Pats. to O'Connor No. 883,335; Ferris No. 1,765,223; Lee No. 2,913,712; Cremer No. 3,090,948; and Lewin et al. No. 3,127,597 relate to various types of shoplifting alarms in connection with the display of various types of merchandise. The idea of intimately associating an alarm system with a chain lock or similar type of night latch is not disclosed in or obvious from these references. None of the aforementioned references discloses the association of a sensor such as a continuity loop with a flexible night latch member such as a chain, in order to activate an alarm when an intruder or attacker tampers with the night latch.

l overcome these disadvantages of the prior art by providing a burglar alarm for use with a conventional chain type night latch or the like by extending a sensing element (forms of which are described hereinafter) either along or through the chain. The sensing element is coupled .to suitable circuitry designed to energize either a local or a remote alarm or a combination of these for the purpose of warning of an intrusion or attempted intrusion, if the chain is broken or if an attempt be made to break the chain. Alternatively, or preferably in conjunction therewith, a sensing element can also be incorporated with the keeper plate or other components of the chain lock to activate such alarm or combination of alarms when the keeper plate or other night latch component is either loosened or removed from its normal location on the entrance door or doorframe.

The sensing element can be colored or textured or otherwise configured to conceal its presence and/or its function in conjunction with the chain lock. When the sensing element takes the form of one or more electrical conductors I contemplate the use of a holding or latching feature in the alarm circuit which will continue the energation of the alarm although the intruder may succeed in splicing or otherwise rejoining the broken ends of the conductors. Alternatively, a number of dummy or superfluous conductors can be added to the energized or functional conductors to make the splicing or other rejoining operation more confusing and less likely, particularly when there is inadequate light for the operation. An electrical shield formed from similar-appearing wires can be disposed adjacentan electrically conductive sensory loop or conductor to obfuscate any attempt at splicing broken conductors. Additional features of my invention involve the use of a spring or other biasing arrangement to make it more difficult to remove the keeper end of the chain from the keeper plate from the outside of the entrance to the premises and to sound an alarm, in any event, should this be accomplished. I also contemplate a switch arrangement incorporated in conjunction with the keeper plate slot such that the alarm system is energized automatically but only when the chain keeper has been inserted into the keeper plate slot by the occupant or occupants of the premises. To minimize the possibility of shock to occupants of the premises, the alarm circuit can be battery-operated or it can be coupled to other sources of low potential electric current, such as a door-chime power supply. If a battery system is used an automatic recharging arrangement can be provided therefor, which can be automatically coupled to the battery when the chain latch is deactivated.

An important advantage of my invention is that it is associated with a familiar and widely used type of night latch and does not require the manipulation of unfamiliar devices of components on the part of the occupants of the premises to energize the alarm system. Instead, the alarm system is incorporated with a conventional latch system and can be energized automatically, whenever the chain latch or similar latch is utilized by the occupants. in certain forms my alarm system can be continuously armed as it is a low-drain system, and peaceful removal of the chain or other connective member from the keeper plate by the occupant is not sensed by the sensory member of the alarm. There is no necessity for the occupants to turn on various activating switches (which can be readily forgotten) when protection is desired and to turn off switches when it is desirable or necessary to deenergize the alarm system. My alarm system is particularly advantageous in this respect, when a remote or external alarm (such as in a police station) is connected to the alarm system. In

other embodiment of my invention, whenever the night latch chain or similar component is attached to utilize the latch, the alarm system is automatically activated or armed and, thus, is not armed continuously. By the same token, the alarm system is disarmed whenever the chain element or other component of the latch arrangement is disengaged. A most significant advantage of my alarm system is the impossibility of disarming the system by an intruder from outside of the entrance door of the protected premises.

It should be noted that the purpose of the usual chain type night latch or other night latchis to protect the occupants of the premises, rather than the premises themselves, as the usual night latch of this type cannot be closed or engaged from outside the entrance. However, it is contemplated that my novel alarm arrangement can be incorporated with various key-operated chain devices and similar locks, which can be engaged and disengaged from outside the entrance of the premises. In such case, the alarm 'circuit of the invention desirably is coupled to a remote alarm such as a building managers office or a nearby police station.

I accomplish these desirable ends by providing an alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, an alarm mechanism, a sensory means extended along at least a portion of said flexible member, and circuit means coupled to said sensory means for energizing said alarm mechanism upon occurence of a malfunction in said sensory means.

I also desirably provide a similar alarm system wherein said sensory means define a circuit path for arming said circuit means, and said circuit means include fail-safe means for energizing said alarm mechanism upon occurrence of a break in said path.

I also desirably provide a similar alarm system wherein said sensory means include an electrically conductive circuit path and electrical shield means extended along said flexible member and adjacent that portion of said path extending along said flexible member, said shield means and said path when shorted together by an attempt to break said flexible member providing said malfunction.

I also desirably provide a similar alarm system wherein switch means are provided for arming and disarming said circuit means, a keeper and keeper plate are provided as part of said latch arrangement, said switch means being located adjacent a slot in said keeper plate so as to be actuated to arm said circuit means upon engagement of said keeper and said keeper plate and to be actuated to disarm said circuit means upon disengagement of said keeper and said keeper plate.

l also desirably provide a similar alarm system wherein said flexible member is a length of chain, and a length of said sensory means is interwoven with and passed along the length of said chain.

During the foregoing discussion, various objects, features and advantages of the invention have been set forth. These and other objects, features and advantages of the invention together with structural details thereof will be elaborated upon during the forthcoming description of certain presently preferred embodiments of the invention and presently preferred methods of practicing the same.

In the accompanying drawings, I have shown certain presently preferred embodiments of the invention and have illustrated certain presently preferred methods of practicing the same, wherein:

FIG. 1 is an elevational view illustrating one form of alarm system arranged in accordance with my invention and in conjunction with a conventional chain latch;

FIG. 2 is an enlarged partial view of a conventional chain latch having another form of my invention incorporated therewith;

FIG. 2A is a still further enlarged, partial view of the alarm system of the invention and similar in its broad outlines to the FIG. 2 arrangement;

- FIG. 2B is a schematic circuit diagram of one form of alarm circuit which can be utilized with the alarm systems of my invention as disclosed therein;

FIG. 2C is a schematic electrical and optical circuit arranged in accordance with my invention and illustrating another form of my novel alarm system;

FIGS. 2 and 3A are partial elevational views of modified forms of a flexible latch member forming part of the invention in these modifications;

FIG. 4 is an elevational view of another form of my alarm system incorporating in this example automatic switch means for arming and disarming the alarm circuit;

FIG. 4A is an elevational and electrical schematic view of still another arrangement of my novel alarm system;

FIG. 5 is an elevational view and circuit diagram of a protected night latch arrangement similar to those illustrated in the preceding figures, but incorporating modified sensing means capable of detecting the loosening or removal of either or both of the anchor plate and the keeper plate of the night latch assembly;

FIG. 5A is an edge view of a portion of the alarm system shown in FIG. 5 and taken along reference line VAVA thereof;

FIG. 5B is a partial elevational view of another form of the invention having a modified flexible member; and

FIG. 6 is a schematic and pictorial arrangement of one form, arranged in accordance with my invention, of alarm circuit which can be utilized with any of the aforementioned alarm systems.

Referring now more particularly to FIGS. 1 and 2 of the drawings the alarm system 11 of my invention, including sensory means, in this case a continuity loop, is associated with a conventional chain lock denoted generally by reference character 14 or other suitable latch arrangement. The chain lock 14 conventionally includes a chain 16 which is somewhat slack when door 18 is fully closed, an anchor plate 20, and a keeper plate 22. The otherwise free end of the chain 16 terminates in a keeper 24, which has a projection 26 (see FIG. 2A) insertable into an enlarged slot portion 28 of keeper slot 30 in the keeper plate 22. Normally, the circuit plate 22 is affixed to the door 18 while the anchor plate is affixed to door frame 32 orto wall surface 34 adjacent thereto.

The alarm circuit 10 can be mounted on the wall 34 adjacent the night latch arrangement 14, as shown in FIG. 1 or as better shown in FIG. 2 the alarm circuit 10 can be remotely located, for example in a bedroom of one or more of the occupants of the premises thus protected. In the arrangement as shown in FIG. 2 the sensor 12' includes conductors 13 connected to the alarm circuit 10. Alternatively, the alarm circuit 10 (or the alarm mechanism 38 (FIG. 28) thereof) can be located outside of the premises serviced by the alarm system 11, (FIG. 1) for example in the managers or house detectives apartment or office of a multi-unit building or in a nearby police or fire station. Alternatively the alarm circuit 10 can be coupled to a pair of alarm mechanisms in parallel, with one of the mechanisms being located within the premises and the other located externally of the premises as foresaid.

The alarm system 11 in accordance with the feature of my invention presently under discussion include a very low-drain circuit 10, which therefore can be left energized or activated continuously. The occupants of the premises are not forced continuously to arm and disarm the circuit 10 as they enter and leave the premises. Suitable circuitry for use as part of the alarm system 11 is described below in connection with FIGS. 28, 2C, and 6 of the drawings.

The sensory means 12, which is coupled to the alarm circuit 10 and forms part thereof is arranged in this example of the invention as a continuity loop, which when subject to a malfunction such as breakage causes the alarm forming part of the alarm system 11 to be energized. Although not essential to the basic feature of my invention, various arrangements can be provided for preventing an intruder from reestablishing the continuity loop 12 and thus terminating the energization of the alarm mechanism.

The sensory means 12, which in this example is in the form of a continuity loop or circuit path can be threaded through the chain 16 of the latch arrangement 14 in such manner as to be unapparent to the casual observer. As better shown in FIG. 2 the loop 12 can be affixed at one end to the chain keeper 24 and adjacent its other-end to anchor plate 20. The loop 12 can be affixed to the keeper 24 by passage through a small hole 35 therein. At the anchor plate 20 the loop can be secured thereto for example by wrapping abouta chain retaining ring 37. Thus, if the chain 16 is severed the continuity of the circuit path 12 is destroyed, which energizes an alarm mechanism in the alarm circuit 10, as described below.

To further conceal the presence of the sensor 12, the latter can be provided with the same color as that of the chain 16. Alternatively the chain 16 can be replaced by a suitable length of a hollow flexible material such as a braided and tubular metal mesh (not shown) through which the sensor 12 can be passed.

Alternatively, again, the chain 16 can be replaced with another flexible member made, as shown in FIG. 58, from conductive loop 12a. The loop 12a can be heavily stranded for strength and flexibility or can be a mixture of copper and steel strands for added strength. The bight of the loop 12a passes through keeper 24a and the other end of the sensor 12a is secured to anchor plate 20a by wrapping about ring 37a and/or by securing to terminals 39. This provides a unitary sensor and flexible member structure, the purpose of which is concealed by insulation 13a.

It is also contemplated that a lock-type chain latch can be substituted for any of the chain latches depicted in the drawings and described herein. As such latches generally unlock the chain at the anchor plate end, it would be desirable to pass the continuity loop or the sensor directly to this end of the chain (or other flexible member) without passage through the anchor ring or in any way securing the sensor to the anchor plate.

As evident from FIGS. 28 and 2C of the drawings (and from FIG. 6 described below), the alarm circuit means 10 and the sensor 12 forming part thereof can be provided in accordance with my invention in a variety of forms. For example as shown in FIG. 2B the alarm circuit 10 comprises a source of electric potential 36, a conventional alarm device 38, such as a bell or buzzer, and a relay coil 40.

The alarm mechanism 38 is coupled across the source 36, which can be a battery as shown or a conventional line voltage connection (not shown), in series with a pair of normally closed contacts 42. The contacts 42, however, are held open in the usual manner by the relay coil 40 when energized. In the arrangement of FIG. 2B the relay coil 40 is normally energized from the source 36 through a dropping resistor 44, and, in this case, both the resistor 44 and the coil 40 are connected in series with the sensor 12. Here, the sensor 12 is a conductive loop or wire arranged to complete a circuit I through the source 36, dropping resistor 44, and the relay coil 40'.

Desirably the dropping resistor 44 is a relatively high resistance for use with a low voltage type relay including thenormally closed contacts 42 and the relay coil 40. Thus, the current drain on the source 36 is very low and the relay coil 40 can be energized continually if desired. Accordingly, as noted above there is no necessity for switching the alarm circuit 10 on and off, and

the alarm system can remain continuously armed.

However, as described below, means in accordance with another featureof the invention are provided for automatically activating and deactivating the alarm circuit l0 orits equivalent.

As noted previously when the chain 16 is broken, the

circuit path including thecontinuity'loop' 12 is also broken, and this deenergizes the relay coil 40. In consequence, the relay contact means 42 are closed and the alarm 38 is energized. It is possible but not extremely likely that the intruder could reconnect the broken ends of the continuity loop 12. To further decrease the possibility of this occurrence the sensing loop can be passed several times through the chain 16 (FIG. 2A) to form, in effect, two or more sensor loops 12 in series. The series loops 12' can be fastened to the anchor plate 20 and keeper 24' in the manner described previously. The series loops l2'can be connected directly through conductors 13' for this purpose to an appropriate one of the alarm circuits described herein. With the use of four or more conductors passing through the chain 16', it is much less likely that the intruder will attempt to locateand reconnect the broken ends.

It is contemplated by my invention that one or more additional sensing members can be employed for or in conjunction with the sensory means 12, as further shown in FIG. 2B of the drawings. The additional sensing arrangement can be in the form of a metallic shield of tubular woven or braided metallic mesh surrounding and extended along at least that portion of the loop 12, which extends along the chain 16. Altematively, one or morenon-looped conductors similarly .ex-

tended along the sensory means 12 can be used. In

either of these cases or in the case of any reasonably equivalent structure, the auxilliary sensing arrangement will be referred to as a shield, in this instance an electrical shield denoted generally by the chain outline 46 thereof in FIG. 2B. Specifically, the shield 46 can take the form of one or more (in this example, three) of the aforementioned conductors, desirably extended or woven through the chain 16 in generally parallel relation to the adjacent portion of the loop 12. The shield 46 is positioned very close and preferably coextensive with that part of the sensory loop 12 which is extended along or through the chain 16.

One end of the shield 46 is connected in series with the dropping resistor 44 and more or less in by-passing relation to the relay coil 40. In the event that a short circuit should occurr between the conductive shield 46 and the conductive sensory loop 12 the relay coil 40 would drop out of the circuit. Such short circuit would not draw a significant current as it would, like the relay coil 40, be in series with the dropping resistor 44. With such malfunction of the sensory means (including the loop 12 and the shield 46) and with the relay coil 40 thus shorted out, the normally closed contacts 42 would permit the alarm mechanism 38 to be energized, as the contacts 42 no longer would be held open by the relay coil 40.

With the use of the auxillary sensing means 46 it is likely that the alarm 38 would be energized before the intruder succeeds in severing the chain 16 or 16, as one or more blows upon the chain 16, particularly with a metal tool or weapon such as a tire iron, would tend to short-circuit the conductive shield 46 to the conductive sensory loop 12. The alarm would not only arouse the occupants of the premises before the intruder succeeds in breaking the chain lock, but also would tend to frighten off the intruder before he succeeded in gaining access to the premises.

The use of the shield 46, in any of its variety of forms, also renders it less likely that the intruder would be able to reattach the broken ends of the sensing arrangement in order to silence the alarm mechanism, when once energized.

Modified forms of the chain lock or similar latch arrangement are shown in FIGS. 3 and 3A of the drawings, and these are arranged to ensure breakage or severance of the continuity loop 12, or equivalent sensory means, prior to actual severance of the night latch chain or other flexible connecting element, by an intruder or attacker. In each of these arrangements the circuit path member 12 is affixed at one end to the chain keeper 24 and adjacent its other end to the anchor plate 20, for example in the manner described above. The chain 16, however, is provided with a relatively stout spring or other expansible resilient member. The expansible member is positioned in and forms part of the chain 16 such that any reasonably hard blow thereof which is substantially less than that required to break the chain will sufficiently elongate the chain, by virtue of the expansion of its expansible member, to break the sensory loop 12. The aforementioned expansible member, illustrated in FIGS. 2 and 3A as a stout spring 48 or 48, can be located adjacent the keeper 24 as shown in FIG. 3 or adjacent the anchor end of the chain 12 as shown in FIG. 3A, or elsewhere along the length of the chain 16. I also consider that the chain spring 48 or 48' can be made longer and less stout so that the flexible member must be stretched slightly to reach the enlarged keeper end of the keeper plate slot 30. It is therefore, much more difficult to remove the keeper 24 from the far end of the slot 30 from the outside of the door 18.

As shown in FIG. 2C, my invention contemplates other forms of sensing means beyond the electrical arrangements noted previously and their equivalents. For example, in the alarm circuit of FIG. 2C a sensory member 50 can form part of an optical circuit and includes an elongated fiber optic bundle, which can'be looped as shown in FIG. 2C and then passed along or through the chain 16, in much the same manner as the electrical conductor loop 12 of FIGS. 1 and 2. For example, the central or return portion of the loop can be affixed to the keeper 24 while the lead in portions of the loop can be wrapped about the anchor ring 37 and then passed to an alarm circuit 52. Of course, a well known characteristic of a fiber optic bundle is its capability of conducting light along a tortuous path.

The alarm circuit 52 is generally similar to a circuit and includes an alarm mechanism 38', potential source 36', relay coil 40, and normally closed relay contacts 42'. In the circuit 52, however, energization of the relay coil 40' is controlled by an electro-optical system including the aforementioned fiber optic sensor 50. Thus, the relay coil 40' is connected electrically in series with the source 36' and with a conventional photoelectric relay 54. A dropping resistor 44' is utilized as before to minimize current drain of the source 36, when the alarm system is on standby or armed. The photoelectric relay includes a pair of normally open contacts 56, which are maintained in the contact closed position as shown by light passing from light source 58 through the'fiber optic loop 50 to photocell 60 forming part of the photoelectric relay 54. Preferably the light source 58 is a low voltage lamp and is likewise connected across the voltage source 36' through a dropping resistor 62 to minimize drain.

The fiber optic loop 50 can be provided with a relatively small diametric dimension and can be otherwise colored or configured so as to be virtually unnoticable when extended through the chain 16 (FIGS. 1 and 2).

When the chain 16 is broken the fiber optic bundle 50 is ofcourse severed with the result that light from the source 58 no longer passes through the bundle 50 to the photoelectric relay 54. The normally open photoelectric relay contacts 56 then open to interrupt the flow of low voltage current to the relay coil 40'. This permits the normally closed alarm relay contacts 42" to close thereby energizing the alarm 38'. As the fiber optic bundle 50 comprises a relatively large number of very fine, light-conducting filaments, it is extremely unlikely that the intruder or attacker can reassemble the broken ends in such manner as to reestablish an adequate-level of illumination at the photocell 60 in order to reenergize the photoelectric relay 54 and thereby to deenergize the alarm 38'.

In conjunction with the feature of my invention as shown in FIG. 2C, I also contemplate the use of means such as the expandible members 48 or 48 of FIG. 3 or 3A respectively to ensure breakage or malfunction of the fiber optic continuity circuit 50 prior to actual breakage of the chain 16 or other connected member.

In the modification of my invention as illustrated in FIG. 4, I provide means for automatically activating and deactivating an alarm circuit 64. The alarm circuit 64 can be provided in the same general arrangement as that of the circuit 10 (FIGS. 1 and 2) or the circuit 52 (FIG. 3C) or the circuit 66 (FIG. 6). The alarm circuit 64, of course, includes battery 67 or other source of suitable electric potential such as the line voltage customarily supplied to the premises. The alarm circuit 64 is coupled in the manner mentioned previously to a suitable sensor 69, which may take the form of one of the sensors described previously.

Automatic activation and deactivation of the alarm circuit 64 is accomplished by a pair of conductive strips 70, 72, which are secured to the entrance door 74 and preferably alligned with and behind the keeper slot 30' of the keeper plate 22'. The contact strips 70, 72 can be spring loaded or otherwise biased toward the keeper slot 30' to ensure contact with the keeper 24, when the latter is inserted into the keeper slot 30 in the usual manner.

As evidenced in FIG. 4 the contact strips 70, 72 are connected in series with the alarm circuit 64 and its source 68, which is preferably a low-voltage source to obviate shock hazard. Thus, the circuit 64 is automatically activated when the keeper 24' is inserted into the keeper plate 22' during use of the latch 14 and is automatically deactivated when the keeper 24' is removed, i.e. when the latch 14' is not in use. A low voltage alarm mechanism (not shown) can be incorporated into the alarm circuit 64, and a dropping resistor 76 can be employed, if desired, further to minimize shock hazard at the contact strips 70, 72. Alternatively or in conjunction therewith that portion of the keeper 24 which is to be grasp by the occupant or occupants of the premises can be electrically insulated (not shown). Other forms of contact means can, of course, be substituted for the contact strips 70, 72. For example one of the contact strips 70, or 72 can be eliminated and the associated conductor 78 or 80 can be electrically connected directly to the keeper plate 22' Where the keeper plate 22' is secured to the door 74, the conductor 78, 80 can be extended across the door in an unobtrusive manner and around one of the door hinges, for example the upper door hinge 82 as shown in FIG. 4, to the source 68 and other components respectively of the alarm circuit 64.

As evident from FIG. 4A, it is not essential that the sensing means be a continuous or reentrant loop insofar as the chain 84 is concerned. In the last-mentioned arrangement of the invention a conductor 'wire 86 is extended from the alarm circuit 10 (the'circuit of FIG. 2B or 6 or equivalent circuit can be utilized for this purpose) to the anchor plate 87. Desirably the conductor 86 is attached to the anchor plate 87 for example by wrapping about anchor ring 88 thereof. From the ring 88 the wire is passed through and along the chain 84 to the keeper 90. The conductor 86 is electrically connected to the keeper 90 as denoted by reference character 92. For this arrangement of the invention, the keeper 90 and keeper plate 94 'are each fabricated from an electrically conductive material. Conductor 96 is electrically connected to the keeper plate 90 and completes the circuit path or continuity loop to the alarm circuit 10', when the keeper is engaged in the keeper plate slot 98.

With the arrangement just described any severance of the chain 84 will also sever the conductor 86 and cause the alarm circuit 10' to energize the alarm mechanism forming part thereof, in the manner described above. The FIG. 4A arrangement in addition will energize the alarm, if a thief succeeds in disengaging the keeper from the keeper plate. The alarm circuit 10' is armed and disarmed by means of manual switch 100 in series with the alarm circuit 10' and a power supply 102 therefor. Alternatively, the alarm circuit can be activated and deactivated automatically for example after the manner of FIG. 4. To ensure electrical contact between the keeper 90 and the keeper plate 94 along the length of the keeper slot 98, a leaf spring 104 or the like can be mounted behind the slot 98 to ensure such electrical contact as the keeper 90 is moved.

In FIGS. 5 and 5A of the drawings modified sensing means are provided for detecting tampering with one or more of the latch components, in addition to the chain 106. In many entrance arrangements it is possible for an intruder to pry loose anchor plate 108 after opening door 110 to the limit permitted by the chain 106. One form of a dual purpose sensing means includes a conductive loop 112 extended through the chain 106 and physically attached to keeper 114 after the manner described previously. However, the conductor loop 112 in this example is interrupted at 116 and one of the ends adjacent the interruption is secured electrically to the anchor plate 108 as denoted by reference character 118. The other end is electrically secured to an electrical contact member 120 secured to a wall or other nonconductive support on which the anchor plate 108 is mounted. When properly mounted the anchor plate electrically engages the contact member 120 to complete the conductive loop 112. Accordingly, the alarm circuit energizes the alarm mechanism forming part thereof when either the chain 106 is broken or when an. attempt is made to pry the anchor plate 108 loose from the wall or other support. If the latching type alarm circuit 66 of FIG. 6 be employed in place of the alarm circuit 10"- only a momentary separation of the conductive anchor plate 108 and the electrical contact 120 is sufficient for continued energization of the alarm mechanism. It is also contemplated that the chain 106 can be provided with a spring such as the spring 48 or 48' mentioned above or other expansible member so that the loop 1 12 is broken when the chain is struck a solid blow. or otherwise pryed or jimmied sufficiently to elongate the expansible member.

It is contemplated that the keeper plate 117, for example, can be more securely fastened to the door than the anchor plate 108 is to the wall of the premises, such that the anchor plate would be preferentially loosened thereby interrupting the continuity loop 112. Alternatively a similar contact arrangement such as chain-outlined contact 119 can be secured between the keeper plate 117 and the door 110. Assuming that the keeper plate 117 is fabricated from a conductive material the keeper plate 117 and the contact 119 likewise can be series-connected to the conductive loop 112 as denoted by chain-outlined conductors 121.

In FIG. 6 of the drawings, the aforementioned latching type alarm circuit is illustrated, as arranged in accordance with another feature of my invention. The alarm circuit 66 of FIG. 6 is shown with latching relay coil 122 in its energized state. Thus, normally open latching contacts 124 are closed while the normally closed alarm contacts l26are open. As in the previously described alarm circuits, the circuit 66 thus incorporates a fail-safe feature. The relay coil 122 is energized as shown from the source 36' by means of a circuit path through dropping resistor 44', latching contacts 124, and sensory means such as continuity loop 12'. If a break occurs in the continuity loop the relay coil 122 is deenergized such that the alarm contacts 126 are closed and the latching contacts 124 are open. The alarm mechanism 38' then is energized continually although the broken ends of the loop 12' may be reconnected. After passage of the emergency or correction of the situation which tripped the alarm circuit, the latching relay 122 can be reenergized by operation of a manual reset switch 128 by an occupant of the premises.

If desired an electrical shield such as the guard wires 46' can be utilized in the alarm circuit 66 after the manner of FIG. 2B. The shield 46' (whenever shorted to the continuity loop 12') is connected in series-parallel with the relay coil 122 and its latching contacts 124 to the source 36'. Thus, a short circuit (limited by dropping resistor 44') between the loop 12' and the electrical shield 46' will short out the relay coil 122 causing its deenergization and concomitant disengagement of the latching contacts 124 and engagement of the alarm contacts 126, without the occurance of a break in the continuity loop 12'. The alan'n mechanism 38, then, will be energized in the case of either type of malfunction in the sensory means, albeit of a momentary character.

From the foregoing it will be apparent that novel and efficient forms of Alarms for Night'Latch have been described herein. While I have shown and described certain presently preferred embodiments of the invention and have illustrated presently preferred methods of practicing the same it is to be distinctly understood that the invention is not limited thereto but may be otherwise and variously embodies and practiced within the spirit and scope of the invention.

I claim:

1. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door to latch said door to said frame, said flexible connective member having a length sufficient to permit opening of said door to a predetermined 2. The combination according to claim 1 wherein said sensory means define a circuit path for arming said circuit means, and said circuit means include fail-safe means for energizing said alarm mechanism upon occurence of a break in said path.-

3. The combination according to claim 1 wherein said sensory means include an electrically conductive circuit path and electrical shield means extended along said flexible member and juxtaposed to that portion of said path extending along said flexible member, said shield means and said path when shorted together by an attempt to break said flexible member providing said malfunction.

4. The combination according to claim 1 wherein switch means are provided for arming and disarming said circuit means, a keeper and keeper plate are provided as part of said latch arrangement, said switch means including at least one conductive strip located adjacent a slot in said keeper plate, said keeper being electrically conductive so as'to arm said circuit means by a circuit path through said keeper and said strip upon engagement of said keeper and said keeper plate and so as to disarm said circuit means upon disengagement of said keeper and said keeper plate.

5. The combination according to claim 4 wherein said switch means include at least one elongated conductive strip substantially coextending with a keeper slot in said keeper plate.

6. The combination according to claim 1 wherein said sensory means include a continuity conductor passed back and forth at least once each way along said flexible member.

7. The combination according to claim 1 wherein said flexible member is a length of chain, and a length of said sensory means is interwoven with and passed along the length of said chain.

8. The combination according to claim 1 wherein said sensory means is secured at spaced positions along its length to the end portionsof said flexible member respectively to aid in creating said malfunction in said sensory means when said flexible member is stretched or broken.

9. The combination according to claim 8 wherein an expansible member is incorporated in said flexible member to ensure malfunctioning of said sensory means upon striking of said flexible member but before severance thereof.

10. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, and circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said circuit means being armed through a photoelectric relay, and said sensory means including a light source and a fiber optic elongated bundle extending from said light source-to said photoelectric relay and along said flexible member. v.

11. An alarm system including alatch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, said flexible connective member having a length sufficient to permit opening of said door to a predetermined extent, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means and to said alarm mechanism for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said flexible member terminating in a conductive keeper, and a conductive keeper plate for detachably securing said flexible member to said other of said door and said frame, said sensory means including electrical conductors electrically connected to said keeper and to said keeper plate respectively so that said keeper and keeper plate are connected in a circuit including said sensory means and so that unauthorized disengagements of said keeper and keeper plate also results in said malfunction.

12. The combination according to claim 11 wherein switch means are provided for said circuit means for disarming said circuit means upon intentional disengagement of said keeper and said keeper plate.

13. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securably to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means for energizing said alarm mechanism uponoccurrence of a malfunction in said sensory means, an anchor member for said flexible member fabricated from a conductive material, an electrical contact inserted between said anchor member and a non-conductive support therefor, and said sensory means including an electrical continuity loop having said anchor member and said electrical contact electrically connected therein so that said sensory means malfunctions upon breakage of said flexible member or upon loosening of said anchor member.

14. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said latch mechanism including a keeper and an elongated keeper plate, said plate having an elongated keeper slot therein, said sensory means including an electrical continuity loop, said keeper and said keeper plate being fabricated from electrically conductive material and being electrically connected in said continuity loop, and biasing means extended along said slot for urging said keeper into electrical contact with said keeper plate as it is moved along said slot.

15. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said sensory means defining a circuit path for arming said circuit means and said circuit means including fail-safe means for energizing said alarm mechanism upon occurrence of a break in said path, said fail-safe means including a relay having normally closed contact means connected in series with said alarm mechanism and a source of electrical potential, said relay having an energizing coil capable of holding said contact open when energized, and said coil being connected in series with said path and said source.

16. The combination according to claim 15 wherein said relay includes normally open contact means connected in series with said path and said coil so that said relay is latched to an open circuit condition upon a momentary break in said path.

17. The combination according to claim 15 wherein electrical shield means are extended along that portion of said path which coextends with said flexible member, said shield means being so connected to said source that said relay coil is dropped from said circuit means when said shield means are short-circuited to said path.

18. The combination according to claim 17 wherein dropping resistance means are connected in said circuit means to said relay coil and to said shield means such that current is limited through said relay coil and said shield means both during normal operation of said coil and when said shield means are short-circuited to said path.

19. The combination according to claim 16 wherein electrical shield means are extended along said flexible member and the adjacent portion of said path, said shield means being connected to said circuit means generally in by-passing relation to said normally open contact means so that said relay is latched to an open circuit condition upon a momentary short circuit between said shield means and said path.

20. An alarm system including a latch mechanism, said latch mechanism being mountable one one of a door frame and an entrance door, an anchor member for said latch mechanism mounted on the other of said door and said frame, an alarm mechanism, electrical sensory. means for mounting between said anchor member and said other of the door and frame, circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means as by loosening or removing said anchor member from said other of the door and frame said anchor member being fabricated from a

Claims (20)

1. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door to latch said door to said frame, said flexible connective member having a length sufficient to permit opening of said door to a predetermined and limited extent, an alarm mechanism, continuous conductive means extended along at least a portion of said flexible member, and circuit means coupled to said continuous conductive means and to said alarm mechanism for energizing said alarm mechanism upon stretching or breaking of the flexible connective member and occurrence of a malfunction in said continuous conductive means.
1. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door to latch said door to said frame, said flexible connective member having a length sufficient to permit opening of said door to a predetermined and limited extent, an alarm mechanism, continuous conductive means extended along at least a portion of said flexible member, and circuit means coupled to said continuous conductive means and to said alarm mechanism for energizing said alarm mechanism upon stretching or breaking of the flexible connective member and occurrence of a malfunction in said continuous conductive means.
2. The combination according to claim 1 wherein said sensory means define a circuit path for arming said circuit means, and said circuit means include fail-safe means for energizing said alarm mechanism upon occurence of a break in said path.
3. The combination according to claim 1 wherein said sensory means include an electrically conductive circuit path and electrical shield means extended along said flexible member and juxtaposed to that portion of said path extending along said flexible member, said shield means and said path when shorted together by an attempt to break said flexible member providing said malfunction.
4. The combination according to claim 1 wherein switch means are provided for arming and disarming said circuit means, a keeper and keeper plate are provided as part of said latch arrangement, said switch means including at least one conductive strip located adjacent a slot in said keeper plate, said keeper being electrically conductive so as to arm said circuit means by a circuit path through said keeper and said strip upon engagement of said keeper and said keeper plate and so as to disarm said circuit means upon disengagement of said keeper and said keeper plate.
5. The combination according to claim 4 wherein said switch means include at least one elongated conductive strip substantially coextending with a keeper slot in said keeper plate.
6. The combination according to claim 1 wherein said sensory means include a continuity conductor passed back and forth at least once each way along said flexible member.
7. The combination according to claim 1 wherein said flexible member is a length of chain, and a length of said sensory means is interwoven with and passed along the length of said chain.
8. The combination according to claim 1 wherein said sensory means is secured at spaced positions along its length to The end portions of said flexible member respectively to aid in creating said malfunction in said sensory means when said flexible member is stretched or broken.
9. The combination according to claim 8 wherein an expansible member is incorporated in said flexible member to ensure malfunctioning of said sensory means upon striking of said flexible member but before severance thereof.
10. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, and circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said circuit means being armed through a photoelectric relay, and said sensory means including a light source and a fiber optic elongated bundle extending from said light source to said photoelectric relay and along said flexible member.
11. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, said flexible connective member having a length sufficient to permit opening of said door to a predetermined extent, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means and to said alarm mechanism for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said flexible member terminating in a conductive keeper, and a conductive keeper plate for detachably securing said flexible member to said other of said door and said frame, said sensory means including electrical conductors electrically connected to said keeper and to said keeper plate respectively so that said keeper and keeper plate are connected in a circuit including said sensory means and so that unauthorized disengagements of said keeper and keeper plate also results in said malfunction.
12. The combination according to claim 11 wherein switch means are provided for said circuit means for disarming said circuit means upon intentional disengagement of said keeper and said keeper plate.
13. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securably to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, an anchor member for said flexible member fabricated from a conductive material, an electrical contact inserted between said anchor member and a non-conductive support therefor, and said sensory means including an electrical continuity loop having said anchor member and said electrical contact electrically connected therein so that said sensory means malfunctions upon breakage of said flexible member or upon loosening of said anchor member.
14. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said latch mechanism including a keeper and an elongated keeper plate, said plate having an elongated keeper slot therein, said sensory means including an electrical continuity loop, said keeper and said keeper plate being fabricated from electrically conductive material and being electrically connected in said continuity loop, and biasing means extended along said slot for urging said keeper into electrical contact with said keeper plate as it is moved along said slot.
15. An alarm system including a latch mechanism, said latch mechanism having a flexible connective member with one end capable of being anchored adjacent one of a door frame and an entrance door and the other end detachably securable to the other of said frame and said door, an alarm mechanism, sensory means extended along at least a portion of said flexible member, circuit means coupled to said sensory means for energizing said alarm mechanism upon occurrence of a malfunction in said sensory means, said sensory means defining a circuit path for arming said circuit means and said circuit means including fail-safe means for energizing said alarm mechanism upon occurrence of a break in said path, said fail-safe means including a relay having normally closed contact means connected in series with said alarm mechanism and a source of electrical potential, said relay having an energizing coil capable of holding said contact open when energized, and said coil being connected in series with said path and said source.
16. The combination according to claim 15 wherein said relay includes normally open contact means connected in series with said path and said coil so that said relay is latched to an open circuit condition upon a momentary break in said path.
17. The combination according to claim 15 wherein electrical shield means are extended along that portion of said path which coextends with said flexible member, said shield means being so connected to said source that said relay coil is dropped from said circuit means when said shield means are short-circuited to said path.
18. The combination according to claim 17 wherein dropping resistance means are connected in said circuit means to said relay coil and to said shield means such that current is limited through said relay coil and said shield means both during normal operation of said coil and when said shield means are short-circuited to said path.
19. The combination according to claim 16 wherein electrical shield means are extended along said flexible member and the adjacent portion of said path, said shield means being connected to said circuit means generally in by-passing relation to said normally open contact means so that said relay is latched to an open circuit condition upon a momentary short circuit between said shield means and said path.
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US4233595A (en) * 1978-11-30 1980-11-11 Christoph Emmerich Kg Chain-type door latch and alarm
FR2466058A1 (en) * 1979-08-15 1981-03-27 Perren Benno self-monitoring alarm system
EP0025815A1 (en) * 1979-09-19 1981-04-01 Philips Kommunikations Industrie AG Method for monitoring extension in stressed components
US4367460A (en) * 1979-10-17 1983-01-04 Henri Hodara Intrusion sensor using optic fiber
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