Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1995-06-05
1996-07-30
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340568, 340665, G08B 1314
Patent
active
055415784
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a sensor capable of detecting when an associated device is being tampered with, and has particular application to the protection of high-priced electrical equipment readily accessible to the public and therefore prone to theft or vandalism.
BACKGROUND ART
A problem currently exists in the security of high-priced electrical equipment, such as computer terminals, electronic printers, photocopying machines, video recording machines and other such items which are often installed in schools and other public places to which numbers of people have relatively free access. Such equipment is prone to theft or vandalism.
Furthermore, retailers stocking and displaying such items suffer from the same problems, attempted and successful illegal removal of electrical and electronic goods being a major source of financial loss to such organisations.
It has been proposed to overcome these problems by physically securing the equipment to an associated bench or table on which it stands, or, in the case of free standing equipment, to the nearest large fixture. However, such action often requires physical alteration to the external casing of the equipment, which can render the guarantee or warranty on the equipment invalid, while the nuts and bolts or flexible cables, chains and the like used to effect the mechanical securement can be removed or clipped through by a determined thief.
Electrical and electronic sensors have also been provided to activate associated alarm systems as and when attempts to remove an associated item are made. More particularly, such sensors may comprise loop alarms including a loop of wire passing through an aperture in the article to be protected and through which an electric current passes. If the loop is broken, as would be necessary to remove the article, an alarm sounds. Such devices suffer from a number of disadvantages, not the least of which is that an item to be protected must include an aperture through which the loop can pass.
It has also been proposed to provide electrical and electronic sensors which can be adhered to the outer casing of the item to be protected such that, on attempted removal of the sensor from the item, an associated alarm is activated. Such sensors commonly rely upon the movement of a mechanical member to make or break an associated electric circuit thereby to trigger an alarm, and are usually of relatively complex and bulky construction and are expensive to produce.
Electrical membrane press switches are generally known and are usually of a fairly compact nature, commonly being of a laminar construction. It is also known to utilise a conductive adhesive to secure together the elements of such switches whereby said adhesive provides an electrically conductive path between said elements as well as physically securing the elements together.
DISCLOSURES OF THE INVENTION
It would be desirable to be able to provide a tamper detection sensor of relatively compact, simple and inexpensive construction for adhesion to an associated item to be protected in such a manner that any tampering with the sensor or attempted removal thereof from the item gives an immediate warning of such activities.
According to the present invention there is provided a tamper detection sensor comprising a substrate of an electrically insulating material to one side of which is applied an electrically conductive material including elements electrically isolated from one another, an electrically conductive bridge member interconnecting said elements and being secured to said elements by an electrically conductive adhesive, and a layer of electrically non-conductive adhesive applied to said one side of the substrate to encase said elements and bridge member and by which the sensor can be secured to an item to be protected, the arrangement being such that, on relative movement between the substrate and the layer of non-conductive adhesive, the conductive adhesive is deformed whereby the electrical resistance thereof is altered, said alteration in res
REFERENCES:
patent: 3932857 (1976-01-01), Way et al.
patent: 4000488 (1976-12-01), Ephraim
patent: 4772878 (1988-09-01), Kane
patent: 5237307 (1993-08-01), Gritton
patent: 5406263 (1995-04-01), Tuttle
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