Motion sensor: A motion sensor is used for movement detection. There are 3 sensor technologies that are used to detect motion: passive infrared, ultrasonic and microwave. The passive infrared motion sensor works by detection of the body heat. The infrared radiation cannot be seen by human as its wavelength is longer than a visible light. Any objects that generate heat also generate infrared radiation. Passive infrared motion sensor monitors the temperature and search for changes in infrared spectrum. This type of motion sensor is commonly used in indoor environment. For instance, motion sensor is linked to a light switch and when it detects presence of person, the light is switched on automatically.