Patent ID: 6650241
Filing Date: 2003-11-18
Classification: G08B

Abstract:
A perimeter monitoring system for detecting and monitoring the presence of at least one monitored device within at least one perimeter, comprising:said at least one monitored device comprising: a transmitter having: an identification generator for providing a unique identification stream corresponding to said transmitter; a random interval generator for minimizing collisions of concurrent transmissions from multiple montiored device by aperiodically activating said identification generator at random intervals; and an RF upconverter and at least one antenna for transmitting said unique identification stream as a unique identification signal at the random intervals; and a receiver for detecting at least one monitored device having: a loop antenna with a conductor situated along at least one perimeter forming the loop; an RF downconverter for receiving said transmitted signal from the antenna and outputting said unique identification stream; an identification decoder for detecting said unique identification stream; at least one timer responsive to said identification decoder and associated with said unique identification stream; and a timeout detector; whereby said timer is reinitialized upon the receipt of said identification stream and said timeout detector produces an alarm signal when said timer reaches a predetermined threshold as an indication that said at least one monitored device is no longer within said at least one perimeter.