Motion detectors are a convenient and efficient source for outdoor security lighting. Most units are prewired and preassembled for easier installation. The simplest way to install a motion detector is to replace an existing light with a motion detector light. Having a motion detector included with your light fixture allows the fixture to work automatically. If an object moves, the motion detector switches the light on, and automatically turns the light off after a preset period of time. The light will stay on as long as motion is detected.