This is a simple - easy to build - multi-purpose alarm. Build it yourself using stripboard or veroboard and a few cheap off-the-shelf components. It has a very low stand-by current and is ideal for battery operation.
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Transistor Door Alarm {B} - Photograph

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Door Alarm {B}
Schematic
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Circuit Board

This is a photograph of the transistor based Door Alarm {B}. It has provision for both normally-open and normally-closed input devices. And the standby current is extremely low. So it's ideal for battery operation. Fit it to a door, window, shed, garage, cupboard etc. and it'll alert you to intruders.


A Photo Of Ron J's 
 Transistor Based  
  ''Door Alarm {B}''


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Door Alarm {B}
Schematic
The Rest of Ron's Circuits Write To Ron More Free-to-Use Circuits Circuit Exchange International