Abstract: An apparatus for automatically controlling the operation of a door comprises a microwave transceiver responsive to detect the movement of a randomly moving object and operative to develop a Doppler signal representative of such movement, the Doppler signal being generally sinusoidal with a zero crossing in each cycle, a strobe generator responsive to the Doppler signal and operative to develop a timing pulse upon the occurrence of each such zero crossing, a pair of integrating circuits responsive to the Doppler signal and operative to develop first and second signals of unlike polarity in the absence of the movement and of like polarity in the presence of the movement, a pair of OR gates for detecting the respective polarities of the first and second signals, a sample and hold circuit responsive to the timing pulse and operative to develop a control signal when the first and the second signals are of like polarity, and a relay driver responsive to the control signal and operative to open the door.