Worried someone might intrude on your evil lair? This DIY sonic tripware alarm is easy to build, decently loud, and is perfect for simple hide-and-seek games or establishing a perimeter around whatever you'd like to keep safe.
The video above shows you basically how the whole thing is done, and it's a great way to see it in action. In short though, all you need is a battery operated alarm clock (you'll need to take care to get the right one for the project), some fishing wire, a plastic or wooden clothespin, an Allen key, some foil, an old gift card, some wire, and some electrical tape.
You'll have to check out the full walkthrough (linked below) for the full step by step, but essentially what you're doing is creating a circuit between the foil-wrapped ends of the clothespin and the clock, via the battery compartment. When the clothespin is closed, the circuit closes and the alarm goes off. When the pin's prongs don't connect, the circuit is open and all's well. You'll use a section of that gift card, tied to some fishing wire, to keep the prongs separate. When someone walks by, trips the wire, and yanks out the card wedge, the alarm goes off, letting you know there's an intruder.
It's simple, uses really easy to get off-the-shelf parts, and works like a charm without being overly complicated. Check out the video above, and then look through the walkthrough over at Instructables below.
Sonic Tripwire Alarm [Instructables]
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