Proximity detectors can also rely on changes in capacitance caused by mutual capacitance, or ... What Are Motion Sensor Lights?

http://www.wisegeek.com/what-is-a-proximity-detector.htm

Sensors and Transducers Lecture – Thomas Schlebusch – 16. oktober 2007 and Abstract — In this paper I will present the principles of proximity and motion ...

http://www.thomas-schlebusch.de/content/2007/proximity-sensors.pdf

Active motion detectors send out signals to detect motion. One of the simplest types of ... An active proximity sensor sends out a pulsed signal such as a high-frequency ...

http://www.ehow.com/how-does_5374788_motion-detector-works.html