Infrared sensors are the sensors that work on Infrared sensing technology to detect the motion of objects. There exist two types of sensors which detect motion with the help of Infrared, one is Active Infrared sensor (AIR sensor) and another one is Passive Infrared sensor (PIR sensor). What is a PIR Motion Sensor ? Passive Infrared Sensor (PIR sensor) or PIR motion sensor is the kind of sensor that measures the Infrared radiations released from objects and thus identify them as moving or still objects. This type of motion sensor is only the receptor of infrared waves and does not release any infrared beam like that is done in Active Infrared sensors.