GB2246228A

GB2246228A - Apparatus for the protection of an external alarm housing

Info

Publication number: GB2246228A
Application number: GB9114294A
Authority: GB
Inventors: David Best
Original assignee: Shorrock Ltd
Current assignee: Shorrock Ltd
Priority date: 1990-07-20
Filing date: 1991-07-02
Publication date: 1992-01-22
Also published as: GB9015928D0; GB9114294D0

Abstract

In its first embodiment it comprises a photodetector 18 and a light source 12 enclosed in a flexible barrier 20. This barrier is such that it will collapse under the application of a force e.g. such as in the event of tampering with the alarm by injection of foam. By collapsing it will reduce the amount of light entering the detector and so indicate an alarm condition. In the second embodiment, Figure 2 (not shown) the light source (22) is mounted so that it does not illuminate the detector (24). Both detector and source are placed in a flexible housing (18) which is preferably painted white inside so that a force on the housing will collapse the barrier causing light to reflect into the detector thus indicating an alarm condition. <IMAGE>

Description

APPARATUS FOR THE PROTECTION OF AN EXTERNAL ALARM HOUSING The invention provides apparatus for the protection of an external alarm housing containing a bell or an electronic sounder such that tampering with the housing in an attempt to prevent an alarm signal will be detected and give rise to a tamper signal.

Most simple alarm systems incorporate an audible signalling device, for example, a bell or an electronic sounder. In order that such signalling devices are audible to the greatest number of people these alarms are often mounted externally of the premises to be protected, for example, to an outside wall etc. In order to prevent external factors, for example, inclement weather etc. affecting the operation of such devices, a housing is usually provided around the bell or sounder thereby enclosing and protecting it.

It will be appreciated that the presence of an external housing is also a deterrent to tampering with the bell or electronic sounder in an attempt to prevent it from providing an alarm signal. However, it is possible to silence an external alarm or sounder by injecting foam or similar material into the housing so as to fill the space therein and around the bell or the sounder. Such foam are generally available from D-I-Y outlets for cavity insulation or adhesive purposes. Once injected into the housing the foam expands rapidly and finds its way into all parts of the bell or electronic mechanism and when it is solidified will prevent the bell from operating or will muffle any sound made by it.

In order to prevent or detect such tampering techniques it is known to provide an optical system within the alarm housing. Such an optical system would have a light source and a light detector such that the presence of foam within the bell housing will obscure the source thus preventing the detector from sensing its presence and consequently cause the sounding of an additional alarm. The ingress of insects etc.

into the bell housing can obscure such optical systems thereby giving rise to false alarms.

One obvious way of overcoming such a problem is to provide two or more optical systems to check for false alarm conditions. However, this requires additional expense, and although there is a low risk of such an event occurring, two insects could give rise to the same alarm condition. It would therefore be an advantage to provide a simple method of securing an optical system to prevent false alarm signals caused by insects or other small animals.

It is an object of the present invention therefore to provide a method and apparatus for the protection of an external alarm housing which is resistant to ingress of insects and prevents false alarm signals arising therefrom.

With this object in view the present invention provides apparatus for the protection of an external alarm housing including an audible signalling device comprising a light source and a light detector, said source and detector being at least partially enclosed in a flexible barrier which is arranged such that application of a predetermined force will cause the barrier to collapse thereby permitting a change in the signal received by the detector which is operative to cause the signalling of an alarm condition.

In a first aspect of the invention the light source is continually on and is arranged so as to provide light continuously to the detector, the barrier is arranged such that its collapse will permit the blocking of the light signal from the source to the detector and the absence of this signal will cause the detector to sound an alarm or otherwise signal an alarm or tamper condition.

In a second aspect of the invention the light source is continually on and is arranged so that its light does not enter the detector, with the barrier arranged such that its collapse will cause a reflective surface to be formed such that light from the source will now reach the detector and hence give rise to an alarm signal.

Preferably the flexible barrier is a plastic bags or similar which is operative to at least partially block any transmission of light therethrough. Preferably the bag is completely opaque to light such that the signal will be reflected according to the second aspect of the invention.

The flexible barrier is preferably arranged to enclose both the light source and the detector thus being operative t9 stop the ingress of insects or similar animals between the source and the detector thereby giving rise to a false signal.

Blockage of the signal from the source to the detector may be accomplished by collapsing of the barrier around the source, around the detector only around both the detector and the cource or in the space between the detector and the source.

Advantageously the second aspect of the invention includes a transparent block positioned such that the light opaque barrier will collapse around it thereby forming a reflective surface, the block being arranged such that light from the light source will be reflected from this formed reflective surface into the light detector thereby giving rise to an alarm signal.

The invention will be described further by way of example with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a first preferred aspect of the invention; and Fig. 2 is a perspective view of a second aspect of the invention.

Referring firstly to Fig. 1, a first embodiment of the invention is intended for insertion into a standard alarm housing (not shown) which may include an alarm bell or an audible sounder or other form of audible signalling device (not shown). The apparatus 10 includes a light source 12 attached to a base plate 14 or similar rigid support surface.

The light source 12 is connected via wires 16 to an electric circuit (not shown) providing power for continuous operation of light source 12.

Opposed to the light source 12 is a light detector 18 attached to an alarm circuit (not shown) which is configured such that an alarm will be activated when the detector condition is changed. In this particular embodiment the detector normally detects the presence of light from the light source 12 and thus an alarm will be activated if the detector 18 fails to "see" i.e. detect the light source 12.

Partially enclosing the light source 12 and the light detector 18 is a flexible barrier 20 formed, for example, of a thin plastics material. In the embodiment illustrated the barrier is in the form of a tube enclosing the light source 12 at one end and the light detector 18 at the other end. Thus the tube 20 prevents an insect or an other small animal blocking reception of light from the light source 12 by the detector 18. Thus a false alarm signal cannot be generated by this event.

However, when the housing (not shown) is filled with a foam or similar material the flexible barrier will collapse and the foam or similar material will block the passage of light from the light source 12 to the light detector 18 causing the alarm to be activated. The alarm can be of an audible type or a visual type or could be signalled by radio or telephone to a remote monitoring station.

An alternative embodiment is illustrated in Fig. 2 in which a light source 22 provides light which is beamed relatively upwardly with respect to a light sensor 24 into a transparent acrylic block 26. The light thus passes through the acrylic block 26 and away from the sensor 24 which therefore has a normally inoperative rest condition.

The light source 22, the light detector 24 and the acrylic block 26 are enclosed by a flexible light opaque barrier 28, for example, of a flexible plastic. Preferably the barrier 28 is, at least on its inside, white so as to provide a reflective surface.

It will thus be apparent that the barrier 28 is operative to prevent the ingress of an insect or other similar small animal into the light sensor path. Furthermore the barrier 28 will not be collapsed by the relatively light weight inserted on it by a moving insect.

On injection of a foam (not shown) into a housing (not shown) including this embodiment of the invention the barrier 28 will be collapsed around the acrylic block 26. The white surface thus contacting the acrylic block will provide a reflective surface and light from the light source 22 will be reflected onto the sensor 24. Upon detecting the reflected light the sensor 24 will activate an alarm thus indicating a presence of foam inside the alarm housing.

The invention is not confined to the foregoing details and variations may be made thereto within the scope of the invention.

Claims

1. Apparatus for the protection of an external alarm housing including an audible signaling device comprising a light source and a light detector, said source and detector being at least partially enclosed in a flexible barrier which is arranged such that application of a predetemined force will cause the barrier to collapse thereby permitting a change in the signal received by the detector which is operative to cause the signalling of an alarm condition.

2. Apparatus as claimed in claim 1 in which the light source is arranged so as to provide light continuously to the detector, the barrier is arranged such that its collapse will permit the blocking of the light signal from the source to the detector and the absence of this signal will cause the detector to activate an alarm.

3. Apparatus as claimed in claim 1 in which the light source is arranged so that its light does not enter the detector, and the barrier arranged such that its collapse will cause a reflective surface to be formed such that light from the source will be reflected onto the detector and hence give rise to an alarm signal.

4. Apparatus as claimed in any of claims 1, 2, or 3 in which the flexible barrier is a plastics bag which is operative to at least partially block any transmission of light therethrough.

5. Apparatus as claimed in claim 4 in which the barrier is completely opaque to light such that the light signal will be reflected therefrom.

6. Apparatus as claimed in any preceding claim in which the flexible barrier is arranged to completely enclose both the light source and the detector.

7. Apparatus as claimed in claim 3 in which a transparent block is positioned such that the light opaque barrier can collapse around it thereby forming a reflective surface, the block being arranged such that light from the light source will be reflected from this formed reflective surface into the light detector thereby giving rise to an alarm signal.

8. Apparatus for the protection of an external alarm housing substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.