All objects with a temperature above absolute zero emit heat energy in the form of radiation. Usually this radiation is invisible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose.
This project about Motion Detector based on PIR sensor. When any moving object is detected around 180 degree of PIR sensor , an active high signal triggers the buzzer via Driver unit ULN2003 for the time period of 5 sec and start continuing sensing next motion. The whole circuit Requires Regulated +5 V DC source, supplied by Bridge rectifier, filter capacitor and 7805 regulator.