The Passive Infrared Sensor (PIR) sensor module is used for motion detection. It can be used as motion detector for security systems or robotics. It works on 5V DC and gives TTL output which can be directly given to microcontroller or to relay through a transistor.It consists of pyroelectric sensor and fresnel lens that detects motion by measuring change in the infrared levels emitted by the objects. It can detect motion up to 20ft. This module is very sensitive to change in infrared levels subjected by human movement.