GB2038060A - Intruder alarm - Google Patents

Abstract

The need arises, in security systems, to protect a room, with the intruder detection arrangement inconspicuous. For this purpose, a wall to be protected has embedded in it a mesh of optical fibres with the fibres arranged in a reticulated pattern. Each fibre has a light source at one end and a light detector at the other end. Thus when the wall is breached, one or more fibres is broken, and the cessation of light flow in such fibres is used to give an alarm. If the light sources used are lasers, so as to supply coherent light, the malefactor's efforts to breach the wall modulate the light, which modulation is also used to give an alarm. The arrangement can also be used to protect the fencing of protected areas: in this case the mesh has strength members and is incorporated in or actually forms the fence. <IMAGE>

Description

SPECIFICATION Intruder alarm This invention relates to an arrangement for the detection of intrusion attempts into a protected.

An object of the invention is to provide an arrangement which will give an alarm not only when an intrusion has occurred into a protected area, but also while the attempt to breach it is in progress.

According to the present invention there is provided an arrangement for the detection of an attempt to penetrate a protected area, which includes a network of optical fibre light conductors forming or included in a fence or wall about the protected area, light sources for launching light into the conductors and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt at penetration disturbs the light traversing one or more of the conductors, which disturbance is detected by the light detectors.

According to the present invention there is also provided an arrangement for the detection of an attempt to penetrate a wall, which includes a network of optical fibre light conductors embedded in the wall, light sources for launching light into the conductors, and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt to penetrate the wall disturbs the light traversing one or more of conductors, which disturbance of the light is detected by the light detectors so as to indicate that such an attempt is in progress.

An embodiment of the invention will now be described with reference to the single highly schematic drawing.

In the arrangement shown a mesh of optical fibre conductors is shown, which mesh is embedded in the wall to be protected. As shown the mesh is constructed in the same way as the mesh of a conventional wire fence with square sections to the mesh, and with a straight fibre at each end of the mesh. The squares in the arrangement shown are 1 50 mm across the diagonal.

At one end of each fibre there is a light source while at the other end there is a light detector. If the wall being protected is breached, one or more of the fibres is broken with the result that light is cut off. When this occurs an alarm is given in well-known manner.

If the light sources used are of the coherent type, i.e. lasers, then the malefactor's efforts to breach the wall modulate the light flowing in some at least of the fibres, which enables an alarm to be given before the wall is breached.

Although the above description relates specifically to the application of the invention to the detection of intrusions into a building.

However, the invention is also applicable to detection of penetration of the fencing of secured areas. In such a case the mesh used for the intruduer detection has strength members formed, for instance, of plastics coated steel strain wires. Such strength-protected fibre meshes can then be incorporated into the fence or used as a fence in its own right, e.g. as an inner fence.

1. An arrangement for the detection of an attempt to penetrate a protected area, which includes a network of optical fibre light conductors forming or included in a fence or wall about the protected area, light sources for launching light into the conductors, and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt at penetration disturbs the light traversing one or more of the conductors, which disturbance is detected by the light detectors.

2. An arrangement for the detection of an attempt to penetrate a wall, which includes a network of optical fibre light conductors embedded in the wall, light sources for launching light into the conductors and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt to penetrate the wall disturbs the light traversing one or more of the conductors, which disturbance of light is detected by the light detectors so as to indicate that such an attempt is in progress.

3. An arrangement as claimed in claim 1, wherein the light sources are coherent light sources and the attempted penetration modulates the light in one or more of the conductors, which modulation is detected to indicate that an attempted penetration is in progress.

4. An arrangement as claimed in claim 1, 2, or 3 and wherein if the attempted penetration breaks one or more of the conductors the stopping of the flow of light in that one or more of the conductors is used to initiate an alarm.

5. An arrangement for the detection of an attempt to penetrate a protected area, substantially as described with reference to the accompanying drawing.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Intruder alarm This invention relates to an arrangement for the detection of intrusion attempts into a protected. An object of the invention is to provide an arrangement which will give an alarm not only when an intrusion has occurred into a protected area, but also while the attempt to breach it is in progress. According to the present invention there is provided an arrangement for the detection of an attempt to penetrate a protected area, which includes a network of optical fibre light conductors forming or included in a fence or wall about the protected area, light sources for launching light into the conductors and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt at penetration disturbs the light traversing one or more of the conductors, which disturbance is detected by the light detectors. According to the present invention there is also provided an arrangement for the detection of an attempt to penetrate a wall, which includes a network of optical fibre light conductors embedded in the wall, light sources for launching light into the conductors, and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt to penetrate the wall disturbs the light traversing one or more of conductors, which disturbance of the light is detected by the light detectors so as to indicate that such an attempt is in progress. An embodiment of the invention will now be described with reference to the single highly schematic drawing. In the arrangement shown a mesh of optical fibre conductors is shown, which mesh is embedded in the wall to be protected. As shown the mesh is constructed in the same way as the mesh of a conventional wire fence with square sections to the mesh, and with a straight fibre at each end of the mesh. The squares in the arrangement shown are 1 50 mm across the diagonal. At one end of each fibre there is a light source while at the other end there is a light detector. If the wall being protected is breached, one or more of the fibres is broken with the result that light is cut off. When this occurs an alarm is given in well-known manner. If the light sources used are of the coherent type, i.e. lasers, then the malefactor's efforts to breach the wall modulate the light flowing in some at least of the fibres, which enables an alarm to be given before the wall is breached. Although the above description relates specifically to the application of the invention to the detection of intrusions into a building. However, the invention is also applicable to detection of penetration of the fencing of secured areas. In such a case the mesh used for the intruduer detection has strength members formed, for instance, of plastics coated steel strain wires. Such strength-protected fibre meshes can then be incorporated into the fence or used as a fence in its own right, e.g. as an inner fence. CLAIMS

1. An arrangement for the detection of an attempt to penetrate a protected area, which includes a network of optical fibre light conductors forming or included in a fence or wall about the protected area, light sources for launching light into the conductors, and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt at penetration disturbs the light traversing one or more of the conductors, which disturbance is detected by the light detectors.

2. An arrangement for the detection of an attempt to penetrate a wall, which includes a network of optical fibre light conductors embedded in the wall, light sources for launching light into the conductors and light detectors for detecting the light which has traversed respective ones of the conductors, wherein an attempt to penetrate the wall disturbs the light traversing one or more of the conductors, which disturbance of light is detected by the light detectors so as to indicate that such an attempt is in progress.

3. An arrangement as claimed in claim 1, wherein the light sources are coherent light sources and the attempted penetration modulates the light in one or more of the conductors, which modulation is detected to indicate that an attempted penetration is in progress.

4. An arrangement as claimed in claim 1, 2, or 3 and wherein if the attempted penetration breaks one or more of the conductors the stopping of the flow of light in that one or more of the conductors is used to initiate an alarm.

5. An arrangement for the detection of an attempt to penetrate a protected area, substantially as described with reference to the accompanying drawing.