Abstract: A single or a plurality of like transmitters are remotely positioned from a single receiver. Each one of the transmitters has an infra-red sensor that when activated by the heat of a moving object transmits a first single pulse to set the AGC of the single receiver and then when the AGC level is established transmits a series of coded identification pulses at substantially the same gain level as the first pulse to the receiver. The coded pulses identify one of a plurality of channels in the receiver that contain a pre-recorded message relating to the transmitting transmitter. When a channel is selected that pre-recorded message is audible produced by the receiver. Typically, the message will announce the location of the transmitting transmitter to a listener which indicates that there is an intruder detected at the transmitter location.