Sensor for an alarm system

Claim 1

A sensor for initiating operation of an alarm for signaling unauthorized interference with an object, said sensor comprising: piezoelectric material operable in response to vibration thereof to generate a voltage; deflectable substrate means supporting said piezoelectric means, said substrate means having a flat, upper surface; a sensing mass carried by said flat, upper surface of said substrate means for movements relative thereto in each of three orthogonal planes, said sensing mass having a flat face, for seating on said flat upper surface, which flat face has an area substantially smaller than the area of the largest horizontal cross section of said sensing mass; whereby the weight of said sensing mass upon said upper surface is concentrated thereon under the smaller area of said flat face; said sensing mass being operable to deflect said substrate and vibrate said piezoelectric means in response to relative movement between said sensing mass and said substrate means in any of said planes; voltage sensitive means for coupling said piezoelectric material to an alarm circuit for energizing the latter in response to the generation of a voltage of predetermined threshold value by said piezoelectric means; and a housing having walls defining a chamber in which said sensing mass is accommodated, said chamber having a size larger than that of said mass thereby enabling said mass to move relative to said substrate means, said chamber having a size which prevents extreme motion of said mass relative to said substrate means, thereby ensuring that the rest position of said sensing mass is in operative relationship with said substrate means.