@▷ Miniature Loop Alarm circuit | Diagram for Schematic

Miniature Loop Alarm circuit

This is a very simple and cheap alarm which require very small power consumption, you may use 9V battery to run this circuit. It uses two transistors to drive the buzzer.

Miniature loop alarm schematic diagram 300x143 Miniature Loop Alarm circuit

The buzzer will sound until you turn the whole circuit off or connect the wire loop back to the jumpers. The same goes for the two LEDs, each indicating its own zone.

For transistors, you can use any NPN general-purpose audio amplifiers/switches (BC 107/108/109, BC 237/238, 2N2222, 2N3904…etc)

Miniature Loop Alarm circuit
source: http://www.zen22142.zen.co.uk/Circuits/Alarm/alarm.html

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