Patent ID: 6150923
Filing Date: 2000-11-21
Classification: G08B

Abstract:
An alarm system for detecting attempted theft of an article, said alarm system including means incorporated in the article itself and arranged to transmit and to continue transmitting an alarm signal when the article is removed from an original location thereof, or disturbed, said alarm system including a generator so arranged that, when triggered, said generator generates an audible alarm signal at random or pseudo-random intervals or produces a random or pseudo-random pattern of longer and shorter bursts of alarm signal arranged to occur at different time intervals, said generator including a sounder device having a chamber including a cap receiving a piezo-electric disc of a diaphragm forming at least part of a chamber wall of said chamber, said cap having a wall provided with an aperture arranged for the passage of sound waves between a baffle outside said chamber and opposing said aperture, said baffle including a plate spaced by a structure extending between said plate and said cap wall by a small gap defining with said cap wall a peripherally open space radially from the region of said aperture, and a battery for powering said generator, the alarm system being such that said intervals become longer as said battery becomes progressively discharged.