GB2103405A - Burglar alarms - Google Patents

Abstract

An alarm device comprises two members 12, 14 biased by means of a coiled spring 18 away from one another towards a stable position, there being a meta-stable position. A projection 22 and corresponding depression 20 between the members from a detent at which the device may be held in a meta-stable position by the application of an external force. The members 12, 14 are shaped so as to fit within a narrow gap where they may be retained in a meta-stable position. On being dislodged from the gap, for example by unauthorised opening of a door or window, the device springs to its stable position thereby triggering an alarm which may be, for example a pin and cartridge arrangement allowing the device to be independent of any electrical circuit wiring. If preferred, the device may operate a switch to close an electric alarm circuit. <IMAGE>

Description

SPECIFICATION Alarm device This invention relates to an alarm device, and in particular a device capable of giving warning of an unauthorised opening of doors or windows.

But the wide incidents of burglary, security and alarm systems increasingly fitted to domestic premises as well as offices, shops and the like. While many such alarm systems are extremely sophisticated they can also be expensive and require skilled operatives for both fitting and servicing.

The invention seeks to provide a simple and cheap alarm device which can be fixed in place simply by an unskilled user.

According to the present invention there is provided an alarm device which comprises two members biased away from one another towards a stable position, there being a meta-stable position at which the members may be maintained by the application of an external force, the members being shaped so as to fit within a narrow gap where they may be retained in the meta-stable position.

In a preferred embodiment, the members are generally wedge shaped both in plan and elevation and are pivoted to one another to form a "scissors" arrangement. The members are biased away from one another by means of a coil spring arranged between one pair or arms of the scissors arrangement. In this case the stable position is when the coil spring has biased the scissor arrangement as far apart as possible. The meta-stable position may be obtained by providing a detent, for example in the form of a projection and corresponding depression, between these two members. In the meta-stable position the detent prevents the members moving apart from one another under the action of the spring if a small external force is applied to prevent the members springing apart.

In use, the device is manually held in the metastable position and placed in a narrow gap, for example the gap between a window and its frame, or a door and its arc frame, wherein the force applied by the services of the gap maintains the device in its meta-stable position. Should the door or window be opened, thereby widening the gap, the external force is removed and the device springs to the stable position. Audible or visible alarm means may be provided, being actuated in the stable position of the device. For example, a pin and cartridge arrangement may be provided so that a blank cartridge is exploded on the device being sprung to the stable position. This has the advantage that no external wiring, batteries, or the like are necessary in order for the device to operate.However, if preferred, switching means may be provided at the stable position so that an electrical circuit is actuated to ring an alarm, flash lights, activate a telephone line to the nearest police station, or any of the normal alarm systems employed with conventional burglar alarm layouts.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of a device constructed according to the invention; Figure 2 is a perspective view of a device of Figure 1 approaching a stable position; Figure 3 is a perspective view of the device of Figure 1 approaching the meta-stable position; Figure 4 is a view of the device of Figure 1 in the meta-stable position; Figure 5 is a perspective view of the device of Figure 1 in place in a gap; and Figure 6 is a similar view to Figure 5 of the device in operation.

Referring to the drawings, it can be seen from Figure 1 that the device generally designated 10 comprises a pair of members 12, 14 arranged for pivotal rotation about an axis 16. The members 12, 14 are biased apart by means of a coil spring 18. A detent mechanism is provided in the form of a projection 20 in the member 14 and corresponding depression 22 in the member 12.

Figure 2 illustrates the device close to the fully open or stable position, that is with the spring 18 almost fully extended.

Figure 3 shows the device being moved towards the meta-stable position, and Figure 4 illustrates the meta-stable position in which the projection 20 meets with the corresponding depression 22. Without the application of some external force normal to the general plane of the members, the detent provided by the projection and depression is not sufficient to prevent the members springing apart back towards the stable position. However, relatively light manual pressure on the members 12 and 14 is sufficient to maintain the projection 20 and depression 22 interengaged thereby holding the device in the meta-stable position. In this position the device may be inserted into a gap, such as the gap between a closed door and its frame (Figure 5).The bias of the spring 18, trying to force the members 12, 14 apart, causes the ends of the members 12, 14 within the gap to be forced away from one another in a direction generally normal to the plane of the members by means of the projection 20 attempting to ride out of the depression 22. This thereby provides a positive force causing the outer surfaces of the members 12 and 14to bear against the walls of the gap thus ensuring that the device 10 is firmly held within the gap and resists being dislodged by any movement or vibration of the door.

As can be seen from Figure 6, when the door is opened and the gap widens the external pressure is released and the device springs to the stable position.

In the device illustrated, as can be seen in Figure 4, the member 14 contains a hole 24 for receiving a blank cartridge 26. A firing pin 28 is carried by the member 12 in such a manner that the pin 28 strikes the cartridge 26 on the device springing to the stable position illustrated in Figure 2. This detonates the cartridge thereby giving an audible warning that the door, window, or the like has been opened. Furthermore, where the entry is being effected by an unauthorised person, the sound of a cartridge being fired in close proximity to that person is likely to cause him to take flight and thereby discontinue his unauthorised entry.

As already mentioned, the cartridge 26 could be replaced by, for example, a micro-switch, which can be wired into a more conventional burglar alarm circuit.

A device of the invention, particularly in itself contained form, is simple, cheap and easy to use.

CLAIMS (filed on 14June 1982) 1. An alarm device which comprises two members biased away from one another towards a stable position, there being a meta-stable position at which the members may be maintained by the application of an external force, and the members being shaped so as to fit within a narrow gap where they may be retained in a meta-stable position.

2. A device as claimed in claim 1 in which the members are generally wedge shaped both in plan and elevation and are pivoted to one another to form a scissors arrangement.

3. A device as claimed in either of claims 1 or 2 in which the members are biased away from one another by means of a coil spring arranged between one pair of arms of the scissors arrangement.

4. A device as claimed in any one of claims 1 to 3 in which the meta-stable position is obtained by providing a detent between the two members.

5. A device as claimed in claim 4 in which the detent is in the form of a projection and corresponding depression.

6. A device as claimed in any one of claims 1 to 5 in which audible of visible alarm means are provided being actuated in the stable position of the device.

7. A device as claimed in claim 6 in which a pin and cartridge arrangement is provided so that the cartridge is exploded on the device springing into the stable position.

8. A method of protecting a door, window or other entrance against unauthorised use which comprises manually placing a device according to any one of claims 1 to 7 in the meta-stable position placing it within the small gap between the sides of the entrance and its means of closure whereby, on unauthorised opening of the ciosure, the device springs to its stable position thereby triggering an alarm.

9. An alarm device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. unauthorised entry. As already mentioned, the cartridge 26 could be replaced by, for example, a micro-switch, which can be wired into a more conventional burglar alarm circuit. A device of the invention, particularly in itself contained form, is simple, cheap and easy to use. CLAIMS (filed on 14June 1982)

1. An alarm device which comprises two members biased away from one another towards a stable position, there being a meta-stable position at which the members may be maintained by the application of an external force, and the members being shaped so as to fit within a narrow gap where they may be retained in a meta-stable position.

2. A device as claimed in claim 1 in which the members are generally wedge shaped both in plan and elevation and are pivoted to one another to form a scissors arrangement.

3. A device as claimed in either of claims 1 or 2 in which the members are biased away from one another by means of a coil spring arranged between one pair of arms of the scissors arrangement.

4. A device as claimed in any one of claims 1 to 3 in which the meta-stable position is obtained by providing a detent between the two members.

5. A device as claimed in claim 4 in which the detent is in the form of a projection and corresponding depression.

6. A device as claimed in any one of claims 1 to 5 in which audible of visible alarm means are provided being actuated in the stable position of the device.

7. A device as claimed in claim 6 in which a pin and cartridge arrangement is provided so that the cartridge is exploded on the device springing into the stable position.

8. A method of protecting a door, window or other entrance against unauthorised use which comprises manually placing a device according to any one of claims 1 to 7 in the meta-stable position placing it within the small gap between the sides of the entrance and its means of closure whereby, on unauthorised opening of the ciosure, the device springs to its stable position thereby triggering an alarm.

9. An alarm device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.