Abstract: The present invention pertains to a transmitter for a coded electronic security system. The transmitter includes a modulator which automatically keys the radio frequency oscillator of the transmitter "on" and "off" to provide a pulse coded signal unique to the particular transmitter in the system. One or more remotely located receivers, of the type described herein, is adapted to receive and decode the signal generated by the transmitter of the present invention and to indicate which of the transmitters in the system has activated a signal device attached to the receiver.