GB2083858A

GB2083858A - Improvements in or relating to security devices

Info

Publication number: GB2083858A
Application number: GB8128353A
Authority: GB
Original assignee: Banham Patent Locks Ltd
Current assignee: Banham Patent Locks Ltd
Priority date: 1980-09-19
Filing date: 1981-09-18
Publication date: 1982-03-31
Also published as: GB2083858B

Abstract

The keeper (2) of a mortice lock has a pressure-sensitive electrical alarm switch (8) mounted on a side face that is disposed frontmost in the direction of door opening movement. The keeper is fixed to a striker plate (4) that has transversely elongated screw holes (6) to secure the keeper to the door jamb. Because of the elongation of the holes, when pressure is applied to the door to try to force it open while the lock bolt is seated in the keeper, the striker plate and keeper can move sufficiently to bring the switch against a side face of the mortice in the door jamb and so cause the alarm switch to operate. <IMAGE>

Description

SPECIFICATION Improvements in or relating to security devices This invention relates to pressure-sensitive security devices.

Tread pads incorporating pressure-sensitive electrical switches are known for use as security devices to detect the presence of an intruder, the pads usually being placed along the passageways or stairs of a building where the switches will be operated by the weight of a person treading on the pads. Such devices, however, are operated only after the intruder has gained entry to the building, and it is possible to circumvent them if their presence is visible in any way or if the intruder avoids treading on the obvious areas where -they are likely to be placed.

The present invention provides a door lock or lock part incorporating a pressure-sensitive electrical switch so arranged that, in use, when a bolt or tongue of the lock has been moved to an operative position, the application of pressure to force the door open without retracting the bolt or tongue causes operation of the switch, whereby an alarm can be sounded when an attempt is made to force an entry.

In one particular aspect of the invention, the staple of a mortice door lock has a pressuresensitive electrical switch mounted on an external side face of the staple that is arranged to be disposed transversely to the initial direction of opening of the door to be protected, and the staple is mounted on or is integral with a strike plate that has attachment holes for screws or the like to fix the striker plate and staple in place, said holes being elongated so as to permit relative movement of the striker plate and staple on the application of pressure to force the lock while the lock bolt or tongue is extended into the staple, whereby to cause operation of the electrical switch.

An example of the invention is illustrated in the accompanying drawing, in which: Fig, 1 shows a mortice lock staple and striker plate incorporating a pressure-sensitive electrical switch according to the invention, Fig. 2 is an exploded view of the switch of Fig. 1, and Fig. 3 is an end view of one plate of the pressure-sensitive switch Fig. 1 illustrates a box-like staple 2 and flat striker plate 4, the staple having an open face (not visible in the figure) flush with a corresponding aperture in the striker plate in generally known manner. The striker plate has a series of screw holes 6 by which it is secured to a door jamb with the staple protruding into a mortice cut in the jamb and positioned to receive the bolt or tongue of the associated mortice lock (not shown) on the door.In the present construction, the screw holes are elongated transversely of the door jamb and in the initial assembly the screws are located at those ends of the holes that lie innermost (i.e. at the front) in the direction of door opening.

On the external side face of the staple that likewise lies innermost in the direction of door opening there is mounted a pressure-sensitive electrical switch S comprising two metal plates 10, 1 2 with terminal tags 14 attached, separated by and adhesively attached to a pad 16 of resilient foamed material. One of the metal plates 10 has a series of dimples 18 protruding towards the other plate 12 and these dimples are located over holes 20 punched through the resilient pad. The switch is attached to the staple by a contact adhesive layer of the outer face of one of the metal plates, preferably the flat 1 2. The switch terminals may be wired to any conventional form of alarm unit to operate that unit when the two plates contact each other.

In use, the door jamb is prepared to receive the staple by cutting a mortice of sufficient width to accept both the staple and the attached pressuresensitive switch. The staple is secured in place by the screws driven through the striker plate holes, at the innermost ends of those holes as already mentioned, and the screw pressure will be sufficient to hold the striker plate and staple firmly fixed in place in normal use. In fact, in many instances it is customary for the mortice lock to supplement a spring latch on the door and the bolt or tongue of the spring latch will itself normally form a fixed abutment when the door is closed limiting any movement of the mortice lock relative to the staple that will resuit in side pressure being applied by the lock bolt on the staple.

If, however, an attempt is made to force the door while the mortice bolt or tongue is in its staple, regardiess of whether or not a spring latch bolt or tongue is also operative, sufficient pressure would be applied to force the door from its jamb in an attempt to burst the lock so that a substantial side force is exerted through the mortice lock bolt or tongue onto the staple. When the force is great enough to cause some movement it will move the staple and striker plate inwards as the retaining force of the securing screws is overcome.The frontmost plate 10 of the pressure-sensitive switch will come against the side of the mortice in the door jamb, so that is cannot follow this movement, and as a result the foamed material is compressed and the two switch plates make electrical contact with each other, either through the dimples 18 or through their flanged edges which lie outside the extent of the pad 16. (If the dimples are not required to make electrical contact the pad 1 6 need not be pen'orated.) It is a feature of the illustrated arrangement that the mortice lock itself can be of entirely conventional form, so that it is possible to make use of the invention in already existing installations by simply fitting the new striker plate and staple assembly. This assembly may therefore be manufactured and sold as a separate unit, and it will be seen that by simply inverting it the same assembly can be used on both right-hand and lefthand jambs. It would also be possible to mount the pressure switch on the main part of the lock, i.e. that part carrying the bolt or tongue, but generally it will be preferred to mount it on the part of the lock that is in a fixed position, on the door jamb.

Claims

1. A door lock or lock part incorporating a pressure-sensitive electrical switch so arranged that, in use, when a bolt or tongue of the lock has been moved to an operative position, the application of pressure to force the door open without retracting the bolt or tongue causes operation of the switch.

2. A door lock or lock part according to claim 1 wherein the switch comprises a pair of contact elements that are resiliently urged apart.

3. A door lock or lock part according to claim 2 wherein the switch comprises a pair of plate-like elements having respective electrical terminals and a resilient pad interposed between and secured to the elements.

4. A door lock part according to any one of claims 1 to 3 comprising an opening for receiving a bolt or tongue of the lock when said bolt or tongue has been moved to an extended operative position in use.

5. A staple for use with a door lock and provided with a pressure-sensitive electrical switch, said switch being mounted on a face of the staple that is arranged to be disposed transversely to the direction of initial opening movement of the door for operation by pressure from a bolt or tongue of the lock extended into the staple when force is applied to open the door without withdrawing said bolt or tongue.

6. A staple according to claim 5 for a mortice lock said staple having a plurality of apertures for fixing elements to secure it to a door jamb, said apertures being elongated in the direction of said opening movement, and the electrical switch being mounted on a front face of the staple externally of a receiving opening provided by said staple for the bolt or tongue.

7. A mortice door lock staple having a pressuresensitive electrical switch mounted on an external side face of the staple arranged to be disposed transversely to the initial direction of opening movement of the door, the staple being mounted on or integral with a striker plate having attachment holes for fixing elements to fix the striker plate and staple in place, said holes being elongated so as to permit relative movement of the striker plate and staple on the application of pressure to force the lock while the lock bolt or tongue is extended into the staple, whereby to cause operation of the electrical switch.

8. A door or lock part incorporating a pressuresensitive electrical switch constructed and arranged for use substantially as described herein with reference to the accompanying drawing.