Theft deterrent system with radio transmitters - has each object fitted with transmitter providing alarm signal when carried out of range

摘要

The theft deterrent system employs a radio transmitter, which is incorporated in each protected object, eg a handbag, and a receiver which is carried by the owner. The received signal amplitude is monitored, so that as the distance between the transmitter and the receiver exceeds a given threshold, provided by an amplitude discriminator, an alarm signal circuit is operated. The transmitter may provide HF transmission pulses, which are used as clock signals for the receiver, or the transmitter may provide a modulated signal which is detected by the discriminator of the reception circuit.