How to build A Shed / Garage Alarm

Description

It has an extremely small standby current - making it ideal for battery-powered operation. This is particularly useful where your garage/shed has no mains supply. I've used a 9-volt battery in the diagram - but the circuit will work at anything from 5 to 15-volts. Just choose a Relay and Siren suitable for the voltage you want to use.

Schematic Diagram

It's easy to use. To set the alarm move SW1 to the "set" position. You now have about 10 to 15 seconds to leave the building. When you return and open the door - the green LED will light. You then have about 10 to 15 seconds to move SW1 to the "off" position. If you fail to do so - the relay will energize and the Siren will sound. Of course - you can turn the Siren off at any time by moving SW1 to the "off" position.

Because of manufacturing tolerances - the precise length of any delay depends on the characteristics of the actual components you've used in your circuit. But by altering the values of R5 & R6 you can adjust the Exit and Entry times to suit your requirements. Increasing the values increases the time - and vice-versa.

Stripboard Layout

circuit from http://www.zen22142.zen.co.uk/ronj/sh.html