Introduction: "Last Day" Magnetic Sonic Cube Landmine

UPDATE: It worked! Apparently someone picked it up Monday morning. It went off, and apparently went off for a while. It sounds like they had to disassemble it to shut it up. I'm ridiculously happy with the results.

At my present job, I have been known as something of a crazy hacker. For reasons too complex to explain here I have decided to leave after ten years. This Friday is my last day. I decided to leave a small present behind for anyone trying to scavenge scraps from my old cube.

Several ideas presented themselves to me, but eventually I decided on creating a small alarm that would go off mysteriously when someone moved it. Despite the elaborate title, the design is simple, and not to hard to replicate.

The alarm I used is something I pulled off the scrap dock of the job. It was originally designed to provide an audible alarm for manufacturing machines. Mine is capable of about 80db on a 9v battery, but you could replicate this with a Radio Shack buzzer or other alarm circuit.

The basic idea is to have a box siting on my desk. When someone moves it, an alarm sounds, and won't shut off. This is because the box has a magnetic trigger inside, and when the box was moved from the desk, it was also moved away from the hard drive magnet I planted under the desk, thus triggering the alarm. It will shut off again if they put it back in the same place, but there will *intentionally* not be anything to mark it's position.

Step 1: Parts

You will need:

1 Alarm circuit, buzzer, or other device to make noise.
1 project box or enclosure. Preferably plastic. The alarm I had came in an enclosure already.
1 9v battery, or a power source appropriate for the circuit you are using.
Small momentary switch. I used one out of a mouse. It needs to have a light trigger.
Hard drive magnet, or any other form of rare earth magnet. needs to be strong.
Misc hardware and some ingenuity. A genuine distaste for your co-workers is also handy.

Soldering gun and solder.
Wire stripper and/or wire cutter
Rotary tool

You could make life a lot simpler if you had a magnetically actuated switch laying around you could use, but I rarely have things work out the easy way. I was forced to do it the hard way and create a magnetic switch from a conventional mouse-button switch.

Step 2: The Switch

The only hard part of this was getting the trigger put together and dialed in. I had to mount the switch to the side of the box, then find a small metal bar to act as a lever. Then I attached a metal weight to the other end of the bar. When a magnet is below the box, it pulls the weight down, disconnecting the battery from the alarm. When the magnet is removed, or the box moved, the weight goes up, connecting the alarm to the battery. Check the notes on the pictures.

Step 3: Final Setup

I don't have any fear of this causing much of a panic. It will, in fact, be exactly the sort of thing people expect of me.

The desk I use is your standard cube issue. It has areas underneath where there is only an 1/4 inch or so of metal and material thickness. the magnet sticks to it just fine, and you can feel the magnetic effect clearly through to the top.

A magnet or two will go underneath, and the box over the "sweet spot" on top. I'll plug in the battery and walk.

I'll prob expand on this one more later. Just thought I would throw this one up there for the hell of it for now.