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Tent Alarm

• On a recent camping/kayak trip my tent was rummaged through looking for valuables while I was kayaking in the evening/dusk.  So, I decided to build a tent alarm which lets me set this up on the two tent door zipper pulls.  One pull connects to the dowel rod and the other connects to the switch which is open when the dowel is in place.  If any zipper is opened then the dowel rod is pulled and the switch closes and the smoke detector sounds because I shorted the test button on the smoke detector.

1. Purchase the cheapest smoke detector you can find.  I found one at Home Depot for $4.95.  Open up the detector and short the test button closed.  This was easy to do on this one as the metal lever could be bent and pinned against the wire contact.

2. Then unsolder the + wire from the battery and solder this to one lead of a wire with two leads.  I used an old CD-ROM power cord for an auto cigarette lighter with both ends cut off.  The other lead is soldered to the battery terminal that the + wire came off of.  So, when the wires are closed by a switch at the other end of the lead then power is applied to the smoke detector and it alarms because the test button is closed.

3. The switch is a lever switch from Radio Shack that has a normally open and normally closed contact.  Use the normally open (N.O.) contact so that when the switch is open power is applied to the smoke detector.  Best to use a voltmeter to make sure you get it right.  I used some wood to make an enclosure to house the switch and a dowel rod that closes the switch.  The dowel rod is what is pulled to set off the alarm.

Cheap smoke detector from Home Depot	Two lead wire connected into the smoke detectors battery power.	Lever switch with a dowel rod that keeps the switch closed when engaged.
Just need to get some clips to allow the dowel rod and switch to connect to the zipper pulls.