A PIR sensor (Passive Infrared) is a device that can detect slight changes in the Infrared light spectrum. Its very widely used in alarm systems. The idea is that the human body will disturb the temperature footprint of a room. A PIR sensor can "see" this change in terms of Infrared Radiation.
This simple project is a simple motion-sensing alarm using a PIR and the Arduino board.
This alarm is handy for booby traps and practical jokes, and it 19s just what you 19ll need to detect a zombie invasion! Plus, it 19s all built on a breadboard, so no soldering required!
Follow this link to see the Make page with complete documentation and code