PIR stands for Pyroelectric Infrared Radial Sensor or Passive Infrared Sensor. PIR is an electronic sensor which detects the changes in the infrared light across certain distance and gives out an electrical signal at its output in response to a detected IR signal. It can detect any infrared emitting object such as human beings or animals if it is the range of the sensor, or moves away from the range, or moves within the range of the sensor. PIR Motion Detector Sensor Module. The Passive Infrared Sensor (PIR) sensor module is used for motion detection. It is often referred to used “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 movement of people, animals, or other objects. They are commonly used in burglar alarms and automatically-activated lighting systems.