This is a Pyrolectric sensor (PIR) module which developed for human body detection and is also called Motion Sensor.
A PIR detector combined with a Fresnel lens are mounted on a compact size PCB together with an analog IC , and limited components to form the module. It detect the motion by detecting the changes in the IR levels emitted from the object.
It can be used as motion detector for security systems or robotics. It works from 3.3 V to 5 V DC and gives TTL output which can be directly given to microcontroller or to relay through a transistor.