Electrical device that react to movements with the help of special sensors are called motion detectors. The sensors function either with infrared radiation or electromagnetic or ultraviolet waves. If movement is detected, the motion detector sends a switching signal to other devices such a lamps or alarm systems. Among the most popular models are devices with PIR sensors. The react to deflection changes such as those occurring when a person walks past the sensor. Motion detectors are used in the lighting of outdoor areas such as yard entryways or gardens.