"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.



    • Barbecue Challenge

      Barbecue Challenge
    • Beauty Tips Contest

      Beauty Tips Contest
    • Stone Concrete and Cement Contest

      Stone Concrete and Cement Contest

    121 Discussions


    7 years ago on Step 3

    sort of reminds me of a concept for a senior prank I came up with... (probably won't ever happen due to difficulty level, improbability and ridiculous stakes...)

    build a large robot with several proximity sensors, powerful wheels, and a big, thick steel body. (use an electric wheelchair or something like that.) give it lots of huge batteries to keep it running for a long time (or make it seek out and plug in to outlets, but that could prove difficult). fill it with concrete so that it's somewhere around 500 lbs, then just set it loose in the halls. make it just wander around without hitting anything, maybe make it get angry if it's moved, etc....

    How about adding a relay wired to latch on when power is applied (or if you could find a latching relay use that) I used a relay wired to latch on for my sonic grenade (well prototype rather) and it works great once the "trigger" switch was turned on it stayed on even if you turned the switch off - the only way to stop it is either the hidden reset switch or disconnecting the concealed battery....


    this was great I made one of these out of an old conduit box and a reed switch I left it in the boys bathroom at school and I was across the hall when it went of the person that tripped it ran out and then a crowd gathered outside the bathroom when they figured out that it was harmless they brought it into the hall to try to turn it off and it was equipped with the most annoying buzzer I could find(fire alarm) plus as an added act of hilarity I added 4 dummy switches to throw them off they sat there for half an hour(I had a backup battery)trying different combinations for the switches it wasn't until someone from the wood shop hacked it open with a saw(I hot glued the lid shut so you couldn't simply open it)when they pulled the batteries they figured out how they should have turned it off(btw I used the same triggering system as you)I was sitting in my class trying as hard as I could not to laugh.nobody got anything done because there ears were ringing. just thought id share my sonic tripmine experience

    4 replies
    Saturn V

    8 years ago on Introduction

    I'm going to combine this with the Annoying Beeper so that if the beeping drives them crazy enough to demolish their office, and they find this, the loud alarm will go off, sending a signal to a hidden speaker in the same room. (I took the speaker out of the device so it could be hidden.) That'd be a good "prank" for april Fool's Day. Well, more like revenge. All I need to do is wire up a prototype.


    9 years ago on Introduction

    Imagine having one of these that Rickroll'd people when they picked it up, or if it screamed, that would be freaking hilarious.


    11 years ago on Step 2

    Okaaaaay. Y dont you just make life easier 4 yourselvs and put a magnetic reed N.O. (normally open) switch in the bottom of the case. You can gett any means of buzzers and alarms from radio shack or dick smith's.

    7 replies

    Reply 11 years ago on Introduction

    no offense, but if you can't waltz into you're local electronics dealer and by a 4-cent magnetic reed switch, then you probably just dont have any common sense. However, the build is facinating and I cant understand y u would put yourself through so much strife to do something so simple?


    10 years ago on Introduction

    make one out of a toy car and let a little kid in your school pick it up