Acme Electronics AE-DE-04 Educational Electronic Hobby Kit

Intruder detector circuit is based on the principle of having a transmitter to produce a beam of radiation and a receiver to detect it. If an intruder comes between the transmitter and receiver, the beam is broken and the alarm sounds. We use a beam of infrared radiation, which is invisible to the eye. This makes it impossible for the intruder to notice the beam and avoid breaking it.