The motion sensor itself is an infrared sensor. In fact, the name of the sensor is a Passive InfraRed or PIR detector. It works by constantly monitoring the infrared radiation (IR) in the cameras general field of view. When a sudden change in this radiation occurs, the sensor can detect it, and assumes it is caused by an object in motion. The PIR motion sensor is connected to a relay switch so that when motion is connected, the relay switch turns on the camera to being recording. The recording session ends when either the motion has stopped or after a pre-programmed period of time after the motion has stopped.