My seven year old son wanted to build a door alarm. Obviously it had to be very simple. But of course he wanted it to look "professional" not like a DIY or toy. I came up with a simple design and some easy steps he could follow. Maybe not do it himself, but at least understand.

The basic idea is to take a door contact usually used in alarm devices and connect it to a smoke detector. For convenience (of the parents) an on/off switch should be included.

Collect all parts

You’ll need

– a magnet contact (reed contect), type=NO normaly open
– a smoke detector
– an on/off switch SPST
– cable (1m, 2 wires 0.7mm)
– 9V battery for the smoke detector

Please be sure to get the right type of reed contact. Alarm devices usually use NC (normaly c…

By: wisser

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