Abstract: An intrusion detector system for detecting the presence of moving targets in one or more surveillance zones and activated either by the presence of the moving target or directly by some positive action for transmitting an alarm signal causing the provision of a predetermined number of pulses having predetermined time periods. A tone generator and control circuitry receiving the timed pulses, generates a combination of multiple tones of discreetly different frequencies during the timed pulses, the combination of multiple tones of each timed pulse being of different frequencies than the combination of multiple tones of each other timed pulse, to provide a tone-coded message that is transmitted to a receiver.