The Passive Infrared Sensor (PIR) sensor module is used for motion detection. It is often referred to as "PIR", "Pyroelectric", "Passive Infrared" and "IR Motion" sensor. The module has an on-board pyroelectric sensor, conditioning circuitry and a dome-shaped Fresnel lens. It is used to sense the movement of people, animals or other objects. They are commonly used in burglar alarms and automatically-activated lighting systems.