GB2054227A - Lock assembly incorporating an alarm switch - Google Patents

Abstract

An intruder alarm comprises a microswitch (18) disposed within a latch portion (13) of a door lock (10). A spring steel plate (17) disposed obliquely within the latch portion (13) and fixed along one edge has its opposite free edge separated by a short distance from a switching member (19) of the microswitch (18). A latch bolt (15) extends into an aperture (16) of the latch portion (13) when the door is closed and, in the event of an attempt to force the door open, bears upon the plate (17) and displaces it sufficiently to actuate the switching member (19) and thereby an audible alarm before entry is forced. A screw (21) extends through a bar (20) and engages the plate (17) so that a minimum force required to actuate the switching member (19) may be varied. Similar arrangements may be provided for a door bolt and socket and for a padlock and hasp assembly. <IMAGE>

Description

SPECIFICATION Alarm The invention relates to an intruder alarm for buildings such as houses, shops, offices and factories.

Intruder alarms take various forms and may for example comprise an electrical circuit interrupted by the forcing of a door or window, or an infra-red beam interrupted by the passage of an intruder, or a microwave transmitter and receiver operative to detect doppler frequency shift caused by movement within a surveyed region. Invariably, however, such intruder alarms are actuated after intrusion has taken place.

An aim of the present invention is to provide an intruder alarm which is actuated prior to break-in and before serious damage has been done. A further aim is to provide such an alarm which is substantially immune to accidental actuation.

According to the present invention there is provided an intruder alarm for a door or window, comprising a switch and a resilient arrangement operative to resist actuation of said switch until a predetermined minimum force applied to a lock of said door has been exceeded, said predetermined force being of such a magnitude that the switch is actuated prior to forcing of the lock and opening of the door or window.

The resilient arrangement may comprise a spring steel plate or one or a plurality of helical springs. The switch may be a microswitch actuated after displacement of the resilient arrangement through a predetermined distance and operative to actuate an audible alarm.

Preferably means are provided whereby the predetermined force of the resilient arrangement is adjustable in magnitude. Advantageously the predetermined force, in use, lies in the range 200N to 700N.

The invention will hereinafter be further described by way of example with references to the accompanying drawings in which: Figure 1 is a perspective view of a portion of a door having a Yale type lock with a first embodiment of an alarm constructed in accordance with the invention disposed partially within the lock; Figure 2 is a horizontal cross-section through part of the lock of Fig. 1; Figure 3 is a perspective view of a portion of a door having a bolt and socket for securing the door, the socket being provided with part of a second embodiment of an alarm in accordance with the invention; Figure 4 is a horizontal cross-section through part of the lock of Fig. 3; Figure 5 is a perspective view of a padlock and hasp with part of a third embodiment of an alarm constructed in accordance with the present invention; and Figure 6 is a horizontal cross-section through the hasp and alarm of Fig. 1.

Referring firstly to Fig. 1, a cylinder lock, designated as a whole by the numeral 10 comprises a latch bolt housing 11 mounted on a door 12, and a catch portion 1 3 mounted adjacent housing 11 and on a joint 14. In the closed position of the door 1 2 (as illustrated) the latch bolt 15, shown in broken line form extends through a side aperture 1 6 in the catch portion 1 3. As will be seen more clearly from Fig. 2 the latch bolt 1 5 may engage one side of a spring steel plate 1 7 frictionally secured at one end within a gap between two bars welded to an inside wall of the catch 1 3. A microswitch 1 8 is disposed on one side of the plate 1 7 and has a switching member 1 9 arranged so as to be actuated in the event that the free end of the spring steel plate 1 7 is displaced towards the microswotch 18 by more than a predetermined distance.A bar 20 extends across between opposite sides of the latch 1 3 and a grub screw 21 extends through a screw threaded aperture in the bar 20 and one end of the screw abuts against plate 1 7. By adjusting the screw both the initial tension in plate 1 7 and the predetermined distance travelled before actuation of member 1 9 may be adjusted.

It will be clear that if a force is applied to the door 1 2 in the direction of the arrow in Fig. 2 the flat surface of the latch bolt 1 5 will bear against the free end of the steel plate 19. Since the force required to displace the plate 1 7 sufficient to actuate member 1 9 lies in the range 200N to 700N the switch 1 8 will not be operated and an audible alarm (not shown) controlled by the switch 1 8 will not be activated by the application of normal forces and accidental knocks. However, in the event of an attempted forcing of the door switching member 1 9 will be actuated and an audible alarm given before entry takes place.The early sounding of an alarm in this way has the great advantage-of deterring further effeorts to gain entry so that in most cases an intruder will flee the scene without having even caused damage to property.

A similar arrangement is shown in Fig. 3 for a door bolt. In Fig. 3 a bolt 22 extends between a door 23 and door jamb 24 into a socket 25 in a box-like housing 26 fixed to the door jamb 24. As will be seen more clearly from Fig. 4, a spring steel plate 27 is fixed along one edge by frictional engagement within a gap in a bar 28 welded into a corner of the housing 26. The opposite free edge of the plate 27 lies adjacent the entry aperture of socket 25, and also close to a switching member 29 of a microswitch 30. A vertical bar 31 carries a screw 32 which extends through the bar 31.An end of this screw 32 engages the steel plate 27 so that by turning the screw 32 the sep we 9w te 27 and switching member 29 may be adjusted so that the force required to displace the plate 29 and actuate switching member 29 is in turn altered. The operation of the arrangement of Figs. 3 and 4 is similar to that of Figs. 1 and 2. If force is applied to the door 23 in the direction of the arrow of Fig. 4 then the bolt 22 will engage the steel plate 27. Since a very considerable force must be applied to the plate 27 before actuation of switching member 29 takes place the inadvertent application of force to the door when bolted will not, unless under exceptional circumstances, result in sounding of the alarm (not shown) controlled by microswitch 30.

However, should an attempt be made to force open the door 23, for example by means of a crowbar, the force required to actuate switching member 29 will be reached well before the door is forced open for example by wrenching housing 26 from the jamb 24 to which it is attached. Thus in this case also, an attempt by an intruder to force an entry would result in the early sounding of an alarm which would not only give advance warning of the attempted intrusion but would act as a powerful persuasion to the potential intruder to leave immediately.

Figs. 5 and 6 illustrate a further variation of the invention applied to a padlock and hasp arrangement. The hasp comprises plates 33 and 34 joined by a hinge 35, and a U-shaped steel member 36 which in use projects through an eye 37 in plate 34. The U-shaped member 36 is attached by the ends of its limbs to a plate 38 and the limbs pass freely through apertures in a plate 39. A microswitch 40 which controls an audible alarm (not shown) is disposed in a space between the plates 38 and 39 and is attached to plate 39. Powerful coil springs 41 over the limbs of the U-shaped member 36 urge the plates 38 and 39 apart to a distance determined by flanges 42 on housing side plates 43 welded to plate 39.The microswitch 40 has a switching member 44 arranged adjacent the plate 38 and it will be clear that application of a force to U-shaped member 36 in the direction of the arrow in Fig. 6 will displace plate 38 towards plate 39 against the action of springs 41. In use the assembly comprising member 36, plates 38, 39 and 43, springs 41 and microswitch 40 will be attached for example to a door jamb by means of screws passing through plate 39, with elements to the rear of plate 39 being recessed into the jamb. Plate 33 would, in this case be attached to the door by screws 45. With a padlock 46 through member 36 as illustrated in Fig. 5 it is clear that any attempt to force the door will result in displacement of member 36, and thus also plate 38, relative to plate 39 against the action of springs 41. The force required to overcome the combined action of springs 41 ides n the range 200N to 7GOt'l so that only 9 serious attempt at forced entry will result in displacement of plate 38 sufficiently to actuate switching member 44 of microswitch 40.

Again, in the event of an attempted forced entry the alarm is actuated prior to entry.

Claims (8)

1. An intruder alarm for a door or window, comprising a switch, and a resilient arrangement operative to resist actuation of said switch until a predetermined minimum force applied to a lock of said door or window has been exceeded, said predetermined force being of such a magnitude that the switch is actuated prior to forcing of the lock and opening of the door or window.

2. An alarm as claimed in claim 1 wherein the resilient arrangement comprises a spring steel plate.

3. An alarm as claimed in claim 1 wherein the resilient arrangement comprises one or a plurality of helical springs.

4. An alarm as claimed in any preceding claim wherein means are provided for varying the magnitude of said predetermined force.

5. An alarm as claimed in claim 2 further comprising adjustable screw means operative to act on said plate whereby said predetermined minimum force may be varied.

6. An alarm as claimed in any preceding claim wherein said switch is a microswitch actuated after displacement of the resilient arrangement through a predetermined distance and operative to actuate an audible alarm.

7. An alarm as claimed in any preceding claim wherein the predetermined minimum force lies in the range 200N to 700N.

8. A lock assembly substantially as hereinbefore described with reference to and as illustrated in Figs. 3 and 4 of the accompanying drawings.

8. An alarm as claimed in any preceding claim in combination with a locking arrangement for a door or window.

9. An alarm substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2 of the accompanying drawings.

1 0. An alarm substantially as hereinbefore described with reference to and as illustrated in Figs. 3 and 4 of the accompanying drawings.

11. An alarm substantially as hereinbefore described with reference to and as illustrated in Figs. 5 and 6 of the accompanying drawings.

CLAIMS (28 May 1980)

1. A lock assembly, for a door or window, comprising a bolt housing or mounting from which a bolt projects to engage into a keeper in the locked condition of the assembly, and incorporating an alarm switch adapted to be actuated upon application of force to the assembly of a magnitude such as to attempt forcing open of the door or window, characterised in that the switch is located in the keeper, and by the provision of resilient means operative to resist actuation of the switch until a predetermined applied force has been exceeded, said resilient means comprising a spring steel plate held by one of its edges only, said plate being faced at one side by an actuating member of the switch, and disposed so as to be confronted at its other side by the bolt when the assembly is locked.

2. An assembly as claimed in claim 1 wherein the switch is a microswitch which is actuated after displacement of the free end, remote from its held edge, of the spring steel plate, through a predetermined distance.

3. An assembly as claimed in claim 1 or 2 wherein actuation of the switch is effective to initiate an audible alarm.

4. An assembly as claimed in claim 1, 2 or 3 wherein means are provided for varying the magnitude of the predetermined force.

5. An assembly as claimed in claim 4 wherein said means comprises an adjustable screw pressing on the plate at the side thereof remote from the bolt.

6. An assembly as claimed in any preceding claim wherein the predetermined force lies in the range 200N to 700N.

7. A lock assembly substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2 of the accompanying drawings.