US3626403A - Protective systems and apparatus therefor - Google Patents

Protective systems and apparatus therefor Download PDF

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Publication number
US3626403A
US3626403A US818860A US3626403DA US3626403A US 3626403 A US3626403 A US 3626403A US 818860 A US818860 A US 818860A US 3626403D A US3626403D A US 3626403DA US 3626403 A US3626403 A US 3626403A
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relay
contacts
loop
current
series
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Goodwin Alfred George Ive
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/02—Mechanical actuation
    • G08B13/08—Mechanical actuation by opening, e.g. of door, of window, of drawer, of shutter, of curtain, of blind
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/22—Electrical actuation

Definitions

  • a protective system capable of being monitored for day and night use comprising a single electrical loop including a plurality of series-connected contacts arranged to be actuated by an intruder and a relay connected in the loop and arranged to be rendered operative to actuate associated contacts connected in an alarm circuit to indicate the presence of the intruder, selected ones of the contacts having diodes connected across the contacts such that the system can operate in accordance with two different modes.
  • the current flow through the diodes is such that no alarm indication is provided if a series-connected contact spanned by a diode is actuated, while for night use.
  • a switching unit is provided to reverse the direction of current flow through the loop to cause the relay to be rendered operative if any series-connected contact is actuated.
  • This invention relates to protective systems and apparatus therefor such as intruder protection, fire and bandit warning systems including intruder detection and warning devices and fire and bandit warning alarms and detectors capable of providing a warning indication of any abnormal occurrence such as the entry of an intruder into a building, or the outbreak of heat, smoke or fire.
  • a closed electrical circuit loop having wired therein series connected, normally closed contacts associated with doors, windows and the like and arranged to open and close with opening and closing of the doors, windows etc., and parallel-connected, normally open contacts associated with floor pressure mats for instance and arranged to close under pressure.
  • a current flows through the series-connected contacts of the loop to effect energization of an electromagnetic relay until one or more of the series-connected contacts is opened in response to the opening of an associated door or window by an intruder, following which the relay is deenergized to effect actuation of associated relay contacts connected in an alarm circuit such that a warning indication is provided of the presence of the intruder.
  • the application of pressure to a floor mat detector will close the associated parallel-connected contacts to bypass or short" the relay winding thereby actuating the relay contacts in the alarm circuit and again providing an indication of the presence of an intruder. It will be appreciated that such a closed loop protective circuit provides a warning indication also if a short circuit or open circuit condition develops in the loop.
  • Open circuit loops have also been provided having normally open contacts connected across a battery or the like connected in series with the winding of a relay, such that closure of a contact in response to a break-in or similar occurrence effects a short circuit thereby deenergizing the relay winding to provide an indication of the presence of an intruder.
  • a disadvantage of the closed loop system is that when such a closed loop is installed in a building, it is necessary to switchoff the system during those periods when the building is occupied otherwise the alarm circuit would be operative to provide a warning indication each time a door or window was opened or a person closed the contacts of a floor mat detector. However, it is during the switch-off periods that the system may be inadvertently or deliberately damaged and such damage might escape detection until the system is switched on again when all personnel have vacated the building.
  • a further disadvantage of the present system is that the whole system is switched off during those periods when the building is occupied whereas a certain degree of protection may be required during those periods at selected points for instance at basement windows, skylights, rear doors, etc.
  • a second wiring loop is provided but such an arrangement adds considerably to the cost of the overall installation.
  • a further object of the present invention is to provide a protective system and apparatus therefor including a single electrical loop capable of operating in accordance with two different operative modes.
  • a still further object of the invention is to provide a twowire protective loop capable of providing an alarm indication whenever the two wires are wholly or partially short circuited or one or other or both open circuited.
  • a protective system comprising a single electrical loop including a bistate control device having means associated with an alarm circuit and arranged to be actuated in response to a change in the operative state of said bistate control device, the loop being connected to a voltage source and also including a plurality of contacts arranged to be actuated whenever an abnormal situation against which protection is required, occurs, and the loop being arranged to operate in accordance with two alternative operating modes during one of which the current flowing through the loop is sufficient to allow said bistate control device to operate in accordance with a first operative state despite actuation of any of said contacts, and during the second mode the current through the loop being such as to cause the bistate control device to change to the other of said operative states whenever a contact is actuated.
  • a protective system including a closed electrical loop connected across the winding of a relay having contacts connected in an alarm circuit, the loop including a plurality of series-connected contacts arranged to be actuated when an abnormal situation occurs, a respective unidirectional current-conducting device connected across selected ones of said contacts such that the system is capable of operating in accordance with one current-conducting mode and switching means for inhibiting current flow through said unidirectional currentconducting means such that the system operates in accordance with a second current-conducting mode.
  • a protective system as described above wherein an additional relay is included in the loop together with normally open parallel-connected contacts connected in series with impedance means, the arrangement being such that whenever a parallel-connected contact is closed, the current flow through the additional relay is increased to an extent sufiicient to change the state thereof but without effecting any change in the state of said first mentioned relay.
  • a protective loop system as described above having a two-wire loop terminated by impedance means and having a relay means arranged to be actuated whenever a whole or partial short circuit or open circuit condition occurs in the loop, second relay means operable to provide second channel operation and interlocking means associated with the two relay means to prevent operation of the second relay means should such a whole or partial short circuit or open circuit condition occur.
  • FIG. I is a circuit diagram of a conventional "closed loop" intruder alarm system
  • FIG. 2 is a circuit diagram of a closed loop" intruder alarm system according to the present invention.
  • FIG. 3 is a circuit diagram of a closed loop" combined intruder and warning alarm system of the present invention
  • FIG. 4 is a schematic circuit diagram of part of an open loop intruder alarm system
  • FIG. 5 is a circuit diagram of part of an AC-DC circuit for an intruder alarm system and FIG. 6 is a circuit diagram illustrating how the response time of a circuit is utilized to provide an intruder alarm indication.
  • the closed electrical loop includes a plurality of normally closed series-connected contacts CI to C5 which may be associated with windows, doors, etc., and arranged to be opened when the associated door or window is opened, and a pair of normally open parallel-connected contacts M1, M2, which may be associated with contact mats or the like each arranged to be closed when pressure is applied to the respective contact mat.
  • the reference Ws indicates a wire screen provided for protection against intruders at windows, glass doors, etc.
  • the contacts C1 to C5 are connected in series with a relay R1 and contacts M1 and M2 are connected across the relay which is normally energized when the series-connected contacts C1 to C are closed, as shown, and the parallel-connected contacts M1, M2, are open.
  • the relay Rll has associated contacts Rl/l connected in an alarm circuit and the contacts Rl/l are arranged to be actuated upon deenergization of relay R1 to provide an alarm indication of the presence of an intruder, whenever one or more of the contacts C1 to C5 is or are opened, or one or more of contacts M1 M2, is or are closed, or the wire screen Ws is broken.
  • a battery B completes the loop and has a limiting resistor r, connected in series therewith in order to protect the battery when a short circuit occurs.
  • unidirectional current-conducting devices such as semiconductor diodes D1, D2, D5, are connected across the respective series-connected contacts C1, C2, C5, and a further diode D4 is connected in series with parallel-connected contact M2.
  • the polarity of the current flowing through the loop is arranged such that diodes D1, D2 and D5 are forward connected such as to pass current whenever the respective contact C1, C2 or C5 is opened, whilst diode D4 is reverse connected such as to inhibit the passage of current when contact M2 is closed.
  • the relay R1 will be deenergized to actuate contacts RH]. and provide an alarm indication of the brealcin.
  • contact Ml has no diode in series therewith and if the mat associated with contact Ml has pressure applied thereto, the contact M1 will close to short circuit relay R1 thereby deenergizing the relay and actuating contacts R1 /1 to provide an alarm indication.
  • a changeover switch (not shown) is provided whereby the direction of current flow through the loop is reversed.
  • Diodes D1, D2 and D5 will now be reverse-connected and diode D4 will be forward connected.
  • contacts C1, C2 or C5 are opened by opening of the door or window protected thereby, the leakage current through the reverse connected diode will be insufficient to maintain energization of the winding of relay R 1. Accordingly, contacts Rl/l will be actuated to provide an alarm indication of the presence of an intruder.
  • diode D4 is now forward connected, if contact M2 is closed diode D4 applies a short circuit across the relay winding and thus relay R1 is deenergized and the alarm indication given.
  • the circuit operates in the selective and complete" protection modes as described above for intruder protection and for additional fire or bandit protection.
  • the resistance and ampere-tums of coil R2 are chosen such that with both relays R1 and R2 in series, the current passing through the loop is sufficient to energize relay R1 but insufficient to energize relay R2. If necessary, the applied voltage V may be increased to allow for the additional voltage drop across the winding of relay R2.
  • relay R1 will be shunted by the respective resistor r to r
  • the individual ohmic value of resistors r to r is selected such that the shunting effect on relay R1 is insufficient to deenergize this intruder alarm relay R1. Nevertheless, the current which now flows through the resistor is sufficient to effect energization of relay R2 thereby actuating contacts R2/l and, in the case of a fire alarm system, provide an alarm indication of the existence of the fire, heat or smoke.
  • a latching contact R1/2 is provided associated with the reset switch S1. As before, closure of contacts M1 or M2 will effect deenergization of relay R1, but at the same time, the current through the loop is increased due to a virtual short circuit caused by closure of contacts M1 or M2. Consequently, the latching contact R1/2 is included in the circuit to prevent energization of relay winding R2 in response to closure of contacts M1 or M2, and to prevent a false fire alarm or hold-up alarm from being given.
  • the latching contact Rl/2 is actuated to open the loop circuit thereby retaining relay R2 in the deenergized state and preventing an alarm from being given. The loop will remain in the open circuit condition until reset switch S1 is operated.
  • relay R1 When one of the contacts F1 to F4 close in response to the detection of heat, fire or smoke or in response to depression of a bandit" or hold-up" alami switch, relay R1 is not affected and remains energized and the loop circuit remains closed via latching contact R1/2. An increased current then flows due to the short circuit initiated by closure of a contact F1 to F4, and relay R2 is energized to effect actuation of contacts R2/l thereby providing a fire or bandit warning alarm indication.
  • an advantage of the circuit shown in HO. 3 is that since the detection" contacts F1 to F4 have no diodes or similar unidirectional current-conducting devices connected in series or in parallel therewith, the contacts are not polarity sensitive, i.e., they are operative irrespective of the direction of current flow through the loop and thus detection facilities are provided for 24 hours of every day if neces' sary.
  • the invention is in no way limited to the closed circuit loop shown in FIGS. 2 and 3 and an open loop is shown in H0. 4 having parallel-connected contacts M3, M4, connected across the battery 8 and relay Rl.
  • FOr dual-mode operation a semiconductor diode D5 is connected in series with contact M4 and the circuit operates in a similar manner to that part of the circuit already described with reference to F10. 2 and includes contact M2, diode D4 and relay R1.
  • electrolytic capacitors may be used as the unidirectional currentconducting devices, instead of the semiconductor diodes.
  • An electrolytic capacitor will, when connected in circuit with a voltage supply become charged such as to inhibit the flow of current in the circuit. If the polarity of the applied voltage is reversed, the capacitor behaves as an impedance and permits current to flow continuously since the capacitor is no longer being charged.
  • any device which changes the magnitude of the current flowing in a circuit when a change of polarity occurs may be used, and the term unidirectional current-conducting device is to be construed to include any such device.
  • the present invention provides a protective system capable of operating in accordance with two different modes which may be termed conveniently day” and night" modes respectively.
  • the change in mode may be dependent upon a change in the direction of the current flowing through a loop or upon the use of unidirectional current-conducting devices.
  • the change in mode may be effected by means of a change in the applied voltage or by changing the response time of the circuit, which for the purposes of the following explanation, includes the relay winding or windings.
  • a change in the applied voltage may be effected by a. a reversal of polarity, e.g., of the battery B in order to produce a change in the direction of current flow through the loop as already described;
  • a change in the waveform of the voltage signal e.g., from an AC voltage to a DC voltage
  • FIG. 5 a circuit for changing from an AC voltage during the dayto a DC voltage at night is shown in FIG. 5.
  • the series-connected contacts C1, C2, C3, are arranged to be connected in circuit with terminals a, b, of an AC voltage source via switches S2, S3 during the daytime such as to operate in accordance with one circuit mode, and to be connected via switches S2, S3, to terminals c, d, of a DC voltage source for night operation.
  • Contacts C1 and C3 have capacitors C10, C11, shunted thereacross and a parallel-com nected contact M1 is connected across the relay R1.
  • An associated relay contact RI/ 1 is normally closed and arranged to be opened when the relay R1 is deenergized.
  • any contacts which might be opened during daytime use are shunted by resistors such as to render the opening of a respective contact ineffective.
  • resistors such as to render the opening of a respective contact ineffective.
  • the value of the applied voltage is decreased and the additional resistance produced by the opening of a contact, decreases the relay voltage to a value sufficient to cause deenergization thereof.
  • the DC voltage may be derived from a DC power pack supplied from the AC mains.
  • the applied voltage may be increased above the nominal voltage to compensate for the voltage drop across the diodes.
  • the voltage supply during the occupied" periods may be separate from that employed during unoccupied" periods.
  • the former may be derived from a DC powerpack and the latter from a battery.
  • the voltage may be derived from a powerpack with standby battery facilities; this facility being less necessary during occupied" periods when alarms due to a supply failure are unimportant.
  • the diodes connected across the series-connected contacts or connected in series with the parallel-connected contacts of the loop may be mounted separately from the contacts or incorporated within a switch unit, particularly where the contacts may be of the magnetic reed type.
  • a switch unit is described in copending British Pat. application No. 50,385/68 and the switch unit may include a switch and at least one unidirectional current-conducting device and/or impedance means connected in series with or across the contacts of the switch.
  • the relays employed in the present invention may be of any suitable type such as electromagnetic or transistor relays.
  • the loop relay R1 should have low-current consumption and be sufficiently robust not to be operated by vibration.
  • the two relays R1, R2 are chosen to have a predetermined resistance/ampere turn relationship, and the ohmic value of resistors r to r will depend upon the characteristics of the relays R1, R2.
  • the system of the present invention provides complete 24 hour monitoring which implies that relay R1 (FIGS. 2 and 3) is continuously energized, being deenergized only when a detector is operated.
  • This condition is unsatisfactory since the relay may become stuck in the energized condition i.e., an unsafe fault condition.
  • the relay When switching from the occupied" to the unoccupied condition, or vice versa, the relay should preferably be deenergized and an indication of the condition provided. An unsafe relay condition would thus not escape detection. During the momentary period during which the relay was deenergized on test, the alann devices would be switched out of circuit.
  • the present invention relates to fire protection circuits employing either fire detection devices or fire alarm warning devices, or both.
  • Fire detection devices include devices which detect the presence of fire, heat or smoke where fire alarm warning devices are devices which are manually operable push buttons operated to give a warning indication of the existence of an outbreak of fire.
  • the contacts F1 to F4 may include either or both types of device.
  • series-connected contacts have been described with particular application to doors, they may be the contacts of any form of intruder detection device such as for instant invisible infrared ray units ringing the exterior of a building or located within the building.
  • a manually operable control unit for use with the protective system of the present invention is described in copending British Pat. application No. 51,843/68 in which switching mechanism is provided to enable the system to be switched from one operative mode to the other and including locking means for preventing the switchover to the second operative mode whenever a fault or alann condition prevails.
  • the loop comprises only two wires terminated by a resistor and no return to the control unit is required in such an embodiment.
  • Current is arranged to flow through the loop to maintain a transistor relay in the OFF" condition when the loop is operative, i.e., giving complete protection.
  • the transistor is rendered conductive to energize or deenergize the winding of the relay and give an immediate alarm.
  • the term transistor relay is intended to indicate at least one transistor connected in circuit with an electromagnetic relay, but the latter may if required be replaced by a power transistor or other solid-state device such as a siliconcontrolled rectifier.
  • normally closed contacts are associated with doors, windows and like points of entry and the contacts are arranged to be held open when the door or window is close.
  • the contact is closed to effectively short circuit the protective loop.
  • the diodes are connected in series with the contacts and if a resistor is connected in series with the diode, the short circuit current will be limited in value.
  • the value of the resistor is chosen such as to prevent transistor relay from operating but a second transistor relay" is arranged to operate to give second channel operation. By interlocking the two relays, the second one is prevented from operating under short circuit conditions.
  • a protective system comprising a single electrical loop including a bistate control device associated with an alarm circuit, said bistate control device operatively changes from one state to another whenever an abnormal situation against which protection is required occurs, the loop being connected to a voltage source and also including a plurality of detection contacts actuated whenever such abnormal situation occurs; a respective unidirectional currentconducting device connected across at least selected ones of said contacts such that the system is capable of operating in accordance with one current-conducting mode despite actuation of any of said at least selected ones of said contacts and switching means to inhibit current flow through the unidirectional current-conducting devices to permit the bistate control device to change to the other of said operative states whenever any one of said contacts is actuated such that the system operates in accordance with a second current-conducting mode and thereby provides continuous monitoring of the loop.
  • a protective system comprising a single closed electrical loop including the winding of a relay having contacts associated with an alarm circuit, the loop also including a plurality of series-connected contacts arranged to be actuated when an abnormal situation occurs, a respective unidirectional current-conducting device connected across at least selected ones of said contacts such that the system is capable of operating in accordance with one current-conducting mode and switching means to inhibit current flow through said unidirectional current-conducting devices such that the system operates in accordance with a second current-conducting mode.
  • a protective system as claimed in claim 2 wherein said series-connected contacts are each normally closed and arranged to be opened whenever the presence of an intruder is detected, such as to change the state of said relay, said unidirectional current conducting devices each comprising a semiconductor diode connected across a respective seriesconnected contact, such that for said one current-conducting mode, whenever a series-connnected contact is opened, current continues to flow around the loop to maintain the normal state of said relay, and said switching means being arranged to reverse the direction of current flow through the loop such that thereafter during said second currentconducting mode, whenever a series-connected contact is opened, the current flow through the loop is interrupted to change the state of said relay and provide an alarm indication of the presence of an in truder.
  • a protective system as claimed in claim 2 wherein in ad dition to said series-connected contacts, at least one parallelconnected contact is provided with a unidirectional currentconducting device connected in series therewith.
  • a protective system as claimed in claim 2 wherein an additional relay is included in the loop together with a plurality of additional parallel-connected contacts connected in series with impedance means such that when an additional parallelconnected contact is actuated, the current flow through said additional relay is increased to an extent sufficient to change the state thereof but without effecting a change in the state of said first-mentioned relay.
  • a single closed electrical loop for the protective system of claim 2 including a single relay winding connected in series with a DC voltage source and a plurality of series-connected contacts each arranged to provide intruder protection at a respective location and to be actuated by an intruder and selected ones of said series-connected contacts each having a unidirectional current-conducting device connected in paral lel therewith, said unidirectional current-conducting devices being connected such that when the current flows through the loop in one direction opening of one of said selected ones of said series-connected contacts fails to interrupt the current flow through the winding of the relay and switching means for changing the direction of current flow through the loop whereby the unidirectional current-conducting devices thereafter inhibit current flow through the winding of the relay whenever an associated series-connected contact is opened.
  • a single closed electrical loop as claimed in claim 8 including normally-open parallel-connected contacts each arranged to provide intruder protection at a respective specific location and to be closed by an intruder and at least one of said parallel-connected contacts having a unidirectional current-conducting device connected in series therewith and connected such that when the current flows through the loop in one direction closing of an associated contact fails to interrupt the current flow through the winding of the relay, and when said switching means changes the direction of current flow through the loop closing of a contact thereafter interrupts current flow through the winding of the relay.
  • each unidirectional current-conducting device is incorporated within a switch unit containing the respective contacts.
  • each unidirectional current-conducting device is incorporated within a switch unit containing the respective contacts; the said unidirectional device and an impedance means being connected in series with or across the contacts of the switch.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Burglar Alarm Systems (AREA)
  • Alarm Systems (AREA)
US818860A 1968-04-29 1969-04-24 Protective systems and apparatus therefor Expired - Lifetime US3626403A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB20320/68A GB1178957A (en) 1968-04-29 1968-04-29 Improvements in and relating to Electrical Protective Systems

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US3626403A true US3626403A (en) 1971-12-07

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US (1) US3626403A (xx)
BE (1) BE732211A (xx)
CH (1) CH534405A (xx)
DE (1) DE1921519C3 (xx)
FR (1) FR2007221A1 (xx)
GB (2) GB1178957A (xx)
NL (1) NL6906607A (xx)
SE (1) SE350866B (xx)

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US3706987A (en) * 1971-08-23 1972-12-19 Bay Alarm Co Alarm loop circuit system with light-emitting current-detection means
US3765016A (en) * 1971-05-24 1973-10-09 Oak Electro Netics Corp Security system including means for polling the premises to be protected
US3798628A (en) * 1971-09-27 1974-03-19 G Ive Protective systems and apparatus therefor
US3832678A (en) * 1970-11-12 1974-08-27 B Gysell Fire alarm system
US3962696A (en) * 1972-06-15 1976-06-08 Inertia Switch Limited Protective systems
EP0015656A2 (en) * 1979-02-09 1980-09-17 Philip Charles Sefton Improvements relating to security equipment
US4333094A (en) * 1978-12-04 1982-06-01 Homexx International Corp. Swimming pool alarm
US4524349A (en) * 1982-08-09 1985-06-18 Nel-Tech Development, Inc. Security system having detector sensing and identification
EP0551183A1 (en) * 1992-01-06 1993-07-14 Tieng-Fu Lin Detecting and alarm system for detecting short-circuited or broken circuit
US20090140848A1 (en) * 2007-11-29 2009-06-04 Richard Rollins Systems and methods for a property sentinel
US20190172670A1 (en) * 2017-12-06 2019-06-06 Defond Electech Co., Ltd. Detection circuit module for use in detecting an operational status of a household appliance door
US10636274B1 (en) * 2019-01-02 2020-04-28 The Boeing Company Reconfigurable enclosure system with barrier continuity loop intrusion detection
US11566447B2 (en) * 2018-06-22 2023-01-31 Bitron S.P.A. Door-lock device

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US4567471A (en) * 1983-08-08 1986-01-28 Pittway Corporation Monitoring system

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US2944252A (en) * 1957-01-07 1960-07-05 American District Telegraph Co Intruder alarm system
US3010100A (en) * 1958-06-30 1961-11-21 American District Telegraph Co Direct current operated burglar alarm system with alternating current supervision
US2971186A (en) * 1959-06-30 1961-02-07 Ripepi Tony Central warning burglar alarm system
US3254334A (en) * 1963-12-19 1966-05-31 American District Telegraph Co Electrical protection system utilizing reverse polarity line testing with unidirectional current devices having reverse breakdown characteristic
US3287718A (en) * 1964-03-10 1966-11-22 Lloyd S Stensrud Subscriber alarm system
US3286250A (en) * 1964-10-16 1966-11-15 Teitelbaum Menashe Burglar alarm utilizing bi-stable electronic switches
US3351934A (en) * 1965-05-19 1967-11-07 Honeywell Inc Supervised alarm system
US3470554A (en) * 1966-03-09 1969-09-30 Johnson Service Co Intrusion alarm system having authorization capability with tamper detection means

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3832678A (en) * 1970-11-12 1974-08-27 B Gysell Fire alarm system
US3765016A (en) * 1971-05-24 1973-10-09 Oak Electro Netics Corp Security system including means for polling the premises to be protected
US3706987A (en) * 1971-08-23 1972-12-19 Bay Alarm Co Alarm loop circuit system with light-emitting current-detection means
US3798628A (en) * 1971-09-27 1974-03-19 G Ive Protective systems and apparatus therefor
US3962696A (en) * 1972-06-15 1976-06-08 Inertia Switch Limited Protective systems
US4333094A (en) * 1978-12-04 1982-06-01 Homexx International Corp. Swimming pool alarm
EP0015656A3 (en) * 1979-02-09 1981-01-07 Philip Charles Sefton Improvements relating to security equipment
US4310835A (en) * 1979-02-09 1982-01-12 Donald Arthur Arnold Security equipment including trigger circuit
EP0015656A2 (en) * 1979-02-09 1980-09-17 Philip Charles Sefton Improvements relating to security equipment
US4524349A (en) * 1982-08-09 1985-06-18 Nel-Tech Development, Inc. Security system having detector sensing and identification
EP0551183A1 (en) * 1992-01-06 1993-07-14 Tieng-Fu Lin Detecting and alarm system for detecting short-circuited or broken circuit
US20090140848A1 (en) * 2007-11-29 2009-06-04 Richard Rollins Systems and methods for a property sentinel
US20190172670A1 (en) * 2017-12-06 2019-06-06 Defond Electech Co., Ltd. Detection circuit module for use in detecting an operational status of a household appliance door
US10964499B2 (en) * 2017-12-06 2021-03-30 Defond Electech Co., Ltd. Detection circuit module for use in detecting an operational status of a household appliance door
US11566447B2 (en) * 2018-06-22 2023-01-31 Bitron S.P.A. Door-lock device
US10636274B1 (en) * 2019-01-02 2020-04-28 The Boeing Company Reconfigurable enclosure system with barrier continuity loop intrusion detection

Also Published As

Publication number Publication date
FR2007221A1 (xx) 1970-01-02
CH534405A (fr) 1973-02-28
BE732211A (xx) 1969-10-01
GB1178957A (en) 1970-01-28
NL6906607A (xx) 1969-10-31
GB1296672A (en) 1972-11-15
DE1921519C3 (de) 1979-12-20
DE1921519A1 (de) 1970-08-27
SE350866B (xx) 1972-11-06
DE1921519B2 (de) 1979-04-26

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