Burglar alarm using thyristor and relay
This is a simple Burglar alarm uses a thyristor as the main element and a relay as the output device. The relay can activate a buzzer or a siren.
This light sensitive alarm is very simple and works using, as main components, a transistor, an LDR and a relay.
The alarm activates when the illumination level changes from almost total darkness to a moderately high illumination level. When this happens the alarm is locked and the alarm signal, be it a light or a sound, remains active.