[ladyada] has a freshly-published and amazingly thorough tutorial on passive infrared (PIR) motion sensors. Most often seen in security floodlights and automatic doors, in creative hands these sensors ...

Moderately priced Passive Infrared PIR Sensor modules are now widely available. By using these readymade and pre-configured PIR sensors, even an average electronics hobbyist can construct his/her own ...

Motion sensing is the detection of the change in position of an object relative to its surroundings or vice versa. There are many kinds of motion detector methods: infrared, optics, radio frequency, ...