An object of the present invention is to provide a method of proximity detection based on transmitting at random intervals burst of a RF signal at a power level, and receiving, while not transmitting, a received RF signal. When detecting said received RF signal emitted by a target in range; an alarm...http://www.google.de/patents/US7265665?utm_source=gb-gplus-sharePatent US7265665 - Vehicle proximity alarm system and method
