by side boards 14 and 16 header 18 and floor 22 each transducer acts as a transmitter and receiver of sound pulses and the circuit within which they are included to be hereinafter described provide means for controlling the timing and duration of the pulses in addition to the beams 32 34 and 36 produced by transducers 26 28 and 30 micro wave motion detectors 38 and 40 are mounted on the face of header 18 on opposite sides of the doorway for producing beams 42 and 44 as noted these micro wave motion detectors 38 and 40 are of conventional design and of the type in general use for the opening of sliding doors the wave beams 42 and 44 are capable of being cast over a wide span and length effective to cover an area completely spanning the approach to the doorway opening 12 on both sides thereof as shown by block diagram fig6 ultra sonic transducers 26 28 and 30 and micro wave motion detectors 38 and 40 are incorporated in electrical system 46 which is connected at terminals 48 and 50 to door 24 power operating means not shown the system is so designed as to use either 12 or 24 volts a c for the operation thereof the voltage is full wave rectified by rectifier bridge 52 and then applied to voltage regulator 54 which conditions the voltage to 6 volts d c for operation of all circuits in the system the 60 hz sine wave is used to lock the system to line frequency pulse shaper 56 forms a pulse to drive the trigger.