Patent ID: 6288640
Filing Date: 2001-09-11
Classification: G08B

Abstract:
An intrusion detection system comprising a plurality of sensors each coupled to a respective one of a corresponding plurality of receivers, each receiver having means for receiving from the associated sensor a radio frequency signal having a multiplicity of transmissions at different frequencies within a predetermined frequency spectrum, and being arranged to detect said multiplicity of transmissions, each of the plurality of receivers having computing means for periodically determining, for each of said multiplicity of transmissions, a corresponding signal amplitude measurement, comparing each signal amplitude measurement for each of the different frequencies with at least one preset threshold value and, if the amplitude exceeds the threshold value for a predetermined time period, indicating a potential alarm condition, the system further comprising means (4) for monitoring each of the plurality of receivers for potential alarm conditions and signalling an actual alarm condition when a particular receiver indicates potential alarm conditions for a predetermined number of different transmission frequencies within the same time period.