Abstract: An autodyne motion sensor apparatus and method intended for use with automatic doors comprising, in a preferred embodiment, a phase coherent transceiver (11) incorporating dual demodulators in phase quadrature, means for amplification of the demodulated signals (12 and 13), means for converting the amplified demodulated signals to digital form (14 and 15) for input to a microprocessor, a microprocessor (16), provision for externally generated microprocessor interrupts corresponding to the instantaneous position of the door (17), provision for a uniform series of timing interrupts (18) to be applied to the microprocessor, provision for other microprocessor inputs a) characterizing the position and sense of motion of the door and b) parameter values utilized by the motion detection algorithm executed by the microprocessor, and a microprocessor detection signal output used to actuate the controlled door.