GB2108302A

GB2108302A - Alarm systems

Info

Publication number: GB2108302A
Application number: GB08132131A
Authority: GB
Inventors: Michael Sacks
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-10-24
Filing date: 1981-10-24
Publication date: 1983-05-11

Abstract

An alarm system is used to give warning of unauthorised penetration of a surface such as a window or wall or other structural surface. A layer of conductive material (1, 2) is applied to the surface and its conductivity or other electrical property is monitored with an electrical circuit (6). A change in the monitored property due to penetration of the surface and consequent disruption of the conductive material is detected by the electrical circuit and an alarm indicator (8) is operated. The conductive material may comprise a metal mesh or conductive foil or other material and may be applied over the surface to be protected or alternatively incorporated within same. <IMAGE>

Description

SPECIFICATION Alarm systems This invention relates to an alarm system for use in protecting surfaces against unauthorised penetration thereof.

Alarm systems are known for use in protecting surfaces, such as walls and windows, against breaking and entry therethrough by burglars, such known systems comprising multiple runs of wire extending across the surface to be protected and connected to a control circuit which operates to trigger an alarm in the event that any such wire run is broken. These known systems however may be difficult or expensive to install particularly where it is required to protect all parts of a surface of relatively large area.

An object of the present invention is to provide an improved alarm system which can be installed conveniently and inexpensively even over a surface of relatively large area and which is capable of affording good protection throughout such surface.

According to the invention therefore there is provided an alarm system, for use in protecting a surface against unauthorised penetration thereof, comprising a layer of conductive material arranged to extend over said surface and an electric control circuit adapted to respond to a change in electrical proerties of said layer caused by penetration of breakage thereof.

With this arrangement, due to use of said conductive material in the form of a layer, it will be appreciated that the alarm system can be installed conveniently and inexpensively and such as to give good protection throughout said surface even where this is of relatively large area.

The alarm system may be utilised in any suitable context and for any suitable purpose. Thus, for example, the system may be applied to a wall, floor, ceiling, roof, door or windows of a building such as a shop, office, house or factory especially in the case of partition walls, ceilings, windows and the like which can be readily broken and may constitute a common source of unauthorised entry for a burglar or the like. The system may also be applied to walls and/or windows of cupboards, safes, motor vehicles or surfaces of any other enclosures to be protected against unauthorised breaking and entering.

The said layer of conductive material may comprise a self-supporting sheet fixed over said surface, or a film or skin formed in situ over said surface, or a sheet or film or substance incorporated in the construction of said surface.

Thus, in one embodiment, the said layer comprises a sheet of conductive material in the form of a metal mesh or metal foil, or a sheet of supporting material such as paper or plastics coated with or having bonded thereto or having embedded or otherwise incorporated therein conductive material such as metal wires, metal mesh, metal foil or conductive paint. Such sheet may be of flexible, semi-stiff or rigid form and may be fixed to the said surface by bonding or with pins or screws, or otherwise as appropriate. In the case of bonding the sheet may be adhesive-backed or may be used with a separate adhesive for example a wallpaper paste.

In a further embodiment the said layer is formed by a paint or the like having dispersed therein or otherwise incorporating suitable conductive material, such paint being applied to the said surfaces by brushing or spraying or otherwise.

In a still further embodiment, the said layer comprises wires or other conductive elements embedded in a glass pane forming the said surface.

For example, such conductive elements may be wires of conventional mesh reinforced glass.

In a still further embodiment the said layer comprises conductive material incorporated in a planar building element such as a wall panel, ceiling tile or the like, such element being used as part of a building surface or being fixed oer an existing surface.

The said layer of conductive material may provide a conductive plane the conductivity of which is monitored between two remote parts thereof (for example diametrically opposite corners) with said electrical circuit, it being understood that such conductivity will change in the event that the plane is disrupted by penetration or breakage thereof. It is however also possible to rely on electrical properties other than conductivity. For example, said layer may form one plate of a capacitor the other plate being a close, second layer separated therefrom by an insulating layer in sandwich construction, in this case the electrical circuit being adapted to monitor capacitance changes between said plates.

The said electrical cicuit may take any suitable form and thus for example may comprise a bridge circuit connected to suitable output circuitry such as amplification and switching stages adapted to drive an audible andlorvisual alarm indicator or the like.

Said layer may be utilised as an independent conductive structure of known, fixed shape and dimensions, and terminals may be provided at fixed positions thereon for connection to the said electrical circuit. With this arrangement, connection and setting of the electrical circuit can be simplified.

It is however also possible to use the said layer as a conductive structure of adjustable shape and dimensions this being the case where the layer is inherently of variable form (as in the case of a conductive paint) or where the layer has to be cut, shaped or joined to accommodate the form of the surface to be protected. In this case it will be appreciated that appropriate measures may be required to ensure, for example, proper interconnection of adjoining layers, proper interconnection of the or each layer to the electrical circuit, and proper setting of the circuit.

If desired and as appropriate the said conductive layer may be used in conjunction with or may form at least part of a protective layer capable of resisting penetration.

The invention will now be described further by way of example only and with reference to the accompanying drawings, Figures 'to 4, which are diagrammatic representations of different embodiments of the invention.

Figure 1 shows two sheets 1,2 of a thin flexible metal mesh used to protect a building wall against unauthorised breaking and entry through same. The mesh sheets 1, 2 are bonded or otherwise fixed to an inner surface of the said wall. As shown (e.g. at 3), the sheets are cut and shaped to conform to the size and shape of the said surface and adjacent sheets are linked electrically for example by soldered joints 4. Two mutually remote parts of the inerconnected sheets are joined by soldered leads 5 to an electrical conductivity bridge circuit 6. The output of the circuit is connected to a switch circuit 7 which operates an alarm bell 8.

In use, the circuit is set with the bridge balanced whereupon any appreciable penetration or breakage of the mesh sheets 1,2 such as to appreciably change the conductivity thereof will unbalance the bridge and consequently actuate the bell 8.

Figure 2 shows a conductive sheet 9 which can be used in place of the mesh sheets 1,2 of Figure 1. This sheet 9 comprises a flexible sheet of paper or plastics 10 having on a reverse side thereof thin flexible foil conductors 11 of the printed circuit kind.

The conductors 11 may comprise multiple runs 12 extending between side bus bars 13 and these bus bars 13 may be used for connection to the control circuit 6, 7, 8.

Figure 3 shows a building panel 14 suitable for use as a wall panel or ceiling tile or the like which comprises a wire loop 15 embedded in the material of the panel (e.g. plaster or plastics) and having terminals 16 at opposite corners for connection to a control circuit for example of the kind shown in Figure 1.

Figure 4 shows a conductive layer 17 suitablefor application to a window of a building or vehicle. The layer 17 comprises a thin flexible sheet 18 or tape of transparent plastics material having secured to the reverse side thereof one or more runs of fine wire 19 connected to edge terminals 20. The reverse side of the sheet or tape has a layer of contact adhesive thereon initially protected with a peel-off backing whereby after removal of such backing, the sheet or tape can be fixed to the window to be protected. The terminals can be connected to a control circuit of the kind shown in Figure 1.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

CLAIMS (Filed on 20th Oct, 1982) 1. An alarm system, for use in protecting a surface against unauthorised penetration thereof, comprising a layer of conductive material arranged to extend over said surface and an electrical control circuit adapted to respond to a change in electrical properties of said layer caused by penetration or breakage thereof.

2. A system according to claim 1, wherein said layer of conductive material comprises a selfsupporting sheet fixed over said surface.

3. A system according to claim 1, wherein said layer of conductive material comprises a film or skin formed in situ over said surface.

4. A system according to claim 1, wherein said layer of conductive material comprises a sheet or film or substance incorprated in the construction of said surface.

5. A system according to claim 2, wherein said self-supporting sheet comprises a sheet of metal mesh or metal foil.

6. A system according to claim 2, wherein said self-supporting sheet comprises a sheet of supporting material with conductive material applied thereto.

7. A system according to claim 5 or 6, wherein said sheet is arranged to be fixed to said surface by bonding.

8. A system according to claim 5 or 6, wherein said sheet is arranged to be fixed to said surface with pins or screws.

9. A system according to claim 3, wherein said film or skin is arranged to be formed by a paint having conductive material dispersed therein.

10. A system according to claim 4, wherein said layer comprises conductive elements embedded in a glass pane forming the said surface.

11. A system according to claim 4, wherein said layer comprises conductive material incorpoated in a planar building element.

12. A system according to any one of claims 1 to 11, wherein the said layer of conductive material provides a conductive plane, the conductivity of which is monitored between two remote parts thereof with said electrical circuit.

13. A system according to any one of claims 1 to 12, wherein said electrical circuit comprises a bridge circuit.

14. A system according to any one of claims 1 to 13, wherein said electrical circuit is arranged to drive an audible and/or visual alarm indicator.

15. A system according to claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

16. A surface when protected with a system according to any one of claims 1 to 15.

17. A surface according to claim 16 which is a wall, floor, ceiling, roof, door or window of a building.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. unauthorised breaking and entry through same. The mesh sheets 1, 2 are bonded or otherwise fixed to an inner surface of the said wall. As shown (e.g. at 3), the sheets are cut and shaped to conform to the size and shape of the said surface and adjacent sheets are linked electrically for example by soldered joints 4. Two mutually remote parts of the inerconnected sheets are joined by soldered leads 5 to an electrical conductivity bridge circuit 6. The output of the circuit is connected to a switch circuit 7 which operates an alarm bell 8. In use, the circuit is set with the bridge balanced whereupon any appreciable penetration or breakage of the mesh sheets 1,2 such as to appreciably change the conductivity thereof will unbalance the bridge and consequently actuate the bell 8. Figure 2 shows a conductive sheet 9 which can be used in place of the mesh sheets 1,2 of Figure 1. This sheet 9 comprises a flexible sheet of paper or plastics 10 having on a reverse side thereof thin flexible foil conductors 11 of the printed circuit kind. The conductors 11 may comprise multiple runs 12 extending between side bus bars 13 and these bus bars 13 may be used for connection to the control circuit 6, 7, 8. Figure 3 shows a building panel 14 suitable for use as a wall panel or ceiling tile or the like which comprises a wire loop 15 embedded in the material of the panel (e.g. plaster or plastics) and having terminals 16 at opposite corners for connection to a control circuit for example of the kind shown in Figure 1. Figure 4 shows a conductive layer 17 suitablefor application to a window of a building or vehicle. The layer 17 comprises a thin flexible sheet 18 or tape of transparent plastics material having secured to the reverse side thereof one or more runs of fine wire 19 connected to edge terminals 20. The reverse side of the sheet or tape has a layer of contact adhesive thereon initially protected with a peel-off backing whereby after removal of such backing, the sheet or tape can be fixed to the window to be protected. The terminals can be connected to a control circuit of the kind shown in Figure 1. It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only. CLAIMS (Filed on 20th Oct, 1982)

1. An alarm system, for use in protecting a surface against unauthorised penetration thereof, comprising a layer of conductive material arranged to extend over said surface and an electrical control circuit adapted to respond to a change in electrical properties of said layer caused by penetration or breakage thereof.