Abstract: The collar consists of two legs pivoted to each other at one end by a hinge member and releasably locked to each other at the other end by a key operated lock. The legs are made of shear-resistant material. A radio signal generating and transmitting device and autonomous power supply are housed within the collar. A trigger switch is closed to activate the device upon opening of a flap by the abducted collar wearer, and circuitry including a silicon controlled rectifier, causes activation of the transmitter and characterized by the impossibility of deactivation thereof, short of complete discharge of the power supply, as long as the lock locks the legs of the collar around the wrist, neck or ankle of the wearer.