a closing of the door when an alternating voltage control signal is provided from only one of the circuits 17 18 also the closing control signal being alternating between high and low voltage will be overridden by a low voltage opening control signal received from the other of circuits 17 18 when no movement is detected by either circuit 17 or 18 a high voltage level control signal is provided to circuit 19 this high voltage control signal is provided from a relatively high impedance and can be overridden by either the low voltage control signal which signals door opening or by an alternating voltage control signal which signals door closing motor control unit 19 responds to the high voltage control signal to maintain the door in its current position either open or closed assuming an initial state wherein there is no motion detected by either radar 4 or 5 both circuits 17 and 18 will provide a high voltage control signal to motor control 19 and the door remains in a closed position as a person illustrated as 10 in fig1 approaches the door sensor 4 detects motion toward the door and provides a low voltage signal to motor control 19 overriding the high voltage control signal provided by circuit 18 and causing control 19 to operate motor 7 to open the door as the person 10 passes through the door no motion is detection by either radar 4 or radar 5 and both.