A contactless motion detector, including an oscillator and an amplifier, has an energizing circuit connected across an electronic breakdown device lying in series with a contant-current unit, this series combination receiving pulsating direct current from a supply circuit in parallel with an output thyristor...http://www.google.com/patents/US3932803?utm_source=gb-gplus-sharePatent US3932803 - Electronic monitoring system including contactless motion detector
