Prank Box




About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author ...

The prank box is basically a sealed wooden box with an electric bell inside that is activated by a key switch. Once it is turned on, a relay inside the box is latched and it cannot be turned off without knowing the secret trick (Spoiler Alert:magnets). Quite understandably, a completely sealed box with a ringing bell inside that doesn't seem to stop can quickly become maddening. It is very funny to watch people ponder the implications of the device, reluctantly turn it on, and then stress out when they cannot turn it off. It is even funnier to get panicked emails from your friend in Canada after you mail it to him without any explanation, and he decides to ignore the directions on the box and turn it on.

Step 1: Go Get Stuff

You will need:

(x1) Laser cut 1/4"-thick plywood box template**
(x1) 6V electric bell
(x1) 4 x D battery holder
(x1) Reed switch
(x1) Latching DPDT relay
(x1) Key switch
(x1) 9V battery holder
(x1) 9V battery snap
(x1) 4-40 x 1/2" wood screws
(x8) 8" zip ties
(x1) 4" x 4" x 1/8" matte white acrylic
(x1) Black and red acrylic paint
(x1) 5-minute epoxy
(x1) 30-NF Fastbond contact cement
(x1) Wood glue
(x1) Masking tape
(x1) Red and black wire
(x1) Wood stain and 220 sandpaper (optional)
(x1) Shrink tube

**The laser cut template should be etched (when appropriate) and cut. The "DO NOT INSERT AND TURN KEY" shape should be etched and cut from 1/8" acrylic.

Step 2: Epoxy

Insert the lock into the hole in the front panel from front to back.

Epoxy it firmly in place.

Step 3: Mark

Place the wooden mounting bracket atop the bottom side of the box.

Next, place all of the components atop their designated spots on the bracket. The reed switch does not have a designated spot, but it should line up flush with the edge of the bracket on the side nearest the 9V battery holder.

Mark all of the component's mounting holes with pencils.

Step 4: Glue

Put glue on the inner-side of the bottom of the box.

The bracket then should be placed on top and line up to the edge of the box, such that when the box is put together the reed switch will be flush against the wall of the box.

Clamp it firmly in place and wait for it to dry.

Step 5: Drill

Using a drill press, drill all of the mounting holes with a 1/8" drill bit. It should go deep into the wood, but not pass entirely through.

Step 6: Mount

Lay 2 zip ties vertically across the battery holder's footprint, and another 2 horizontally.

Firmly mount all of the major components to the bracket with screws.

Step 7: Wire It Up

Attach a red wire to the common connections for the reed switch and the key switch.

Attach another red wire to the normally open (NO) connections  on both switches. Connect these two wires to the red wire from the 9V battery clip.

Attach black wires to the two normally closed (NC) connections on both switches. Connect these two wires to the black wire from the 9V battery clip.

In essence what you have just done is create a situation in which ground is always connected in the circuit. By engaging one of the switches, you are introducing a positive voltage. This - in essence - flips the polarity one way or another, and latches the relay open or closed. So, when you turn the key, it latches it closed and keeps the bell ringing. Then, when you engage the reed switch, it flips the polarity and latches it open and turns off the bell.

Before you are done, you need to wire the bell to the D battery holder and the relay.

First, wire together the black wire from the battery holder, to the frame of the bell.

Next, wire the red wire from the battery holder to the center pin on the relay.

Finally, wire the red wire from the battery holder to the coil connection on the bell. This is the mounting terminal not connected to the frame.

Cover all exposed electrical connections with shrink tube.

Step 8: Heat

Blast all of the shrink tube applies in the last step with a heat gun to firmly hold it in place and protect the electrical connections.

Step 9: Batteries

Insert the D batteries in the battery holder.

Using 4 more zip ties, firmly band all of the batteries in place both vertically and horizontally.

Trim the excess zip tie leads.

Step 10: Glue

Plug in the 9V battery and epoxy the battery holder in place in the battery holder.

Hot glue the DPDT relay to the mounting bracket in the free space next to the battery.

Step 11: Clean Up

Bundle all of the loose wires together with zip ties.

If possible, zip tie this bundle to the battery pack in order to prevent it from interfering with the bell.

Step 12: Glue It Together

After you test it to make sure the bell turns on (and off), it is time to seal the box shut.

Apply wood glue to all of the joints and firmly clamp it together.

Step 13: Sand

Using a belt sander, round all of the edges.

Step 14: Make the Sign

Laser cut the sign using the template from Step 2. If you don't have a laser cutter, you can use a service like Ponoko, or do this the old-fashioned way with saws, stencils and Exacto blades.

Once the sign is cut out and stenciled, paint the word "NOT" red, and all of the other words black. Paint the edge of the sign black as well.

When the paint dries, peel away the protective coating from both and pick out the island bits.

Step 15: Sand and Stain (optional)

Sand the box, wipe it clean and put on a coat of stain in a singular direction.

When this is dry, lightly sand again and apply stain in the opposite direction.

Finally, lightly sand once more and lay one last coat of stain in the initial direction.

Step 16: Affix Sign

With masking tape, mask out the spot on the box where you want to place your sign. Apply contact cement to this spot and wait for it to dry.

Apply contact cement to the back of the sign, and wait for this to dry as well.

Carefully align the sign with the box, as you will only get one chance to do this right, and then firmly press them together.

Step 17: Mail It to Canada

Besides the fact that it is simply good to distance yourself from the person who engages the box, I find that Canadians are really bad at following the directions written upon the label.

I don't know if this is on account of the long winters fostering a strong inner life and innate curiosity, or because socialized medicine makes them fearless. Or - perhaps - since everyone in the world loves Canadians, they just assume no one will send them a sealed box with a bell that will not turn off. For all I know, it could be something entirely different in the national character that causes this phenomenon. I am not really sure why they are so susceptible to inserting and turning the key.

It took Mike in Vancouver only a few minutes to insert and turn the key. I can only imagine what must have been running through his mind while he made that decision.

Remember to be a good southern neighbor and eventually tell them how to turn it off. However, I think 20 - 30 minutes is about a fair amount of time to wait before telling them about the magnet triggered reed switch on the side of the box.

Also, when triggering the reed switch, make sure the key is not inserted in lock and turned. If it is, this will not work.

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    123 Discussions


    6 weeks ago

    Hi There,
    Today I failed.. Somehow always when I took out the key my bell stopped ringing. It might be due to the use of a slightly different relais.
    I also realized that a bell with ounly one coil will not work because it is only shoots the hammer once against the bell and stays there.
    I the process of making it work I somehow killed my reed switch so I have to wait to continue...
    In the meantime I made a new circuitplan this sould solve my key is out problem. Does any one have any sugesstions.


    3 months ago

    I CANNOT find a 9v dpdt latching relay anywhere for this. Everyone has them listed as discontinued. OMCRON and Panasonic seem to be the only companies that made them. Any suggestions?

    1 reply

    Reply 2 months ago

    I link to a part on Jameco. It is listed as being discontinued, but they have 197 still in stock.


    3 years ago

    There is one major problem with sending these things through the mail, especially airmail. Think about the emotional climate we live in today. Half of the stuff I used to make as a kid would now be labeled as terroristic items. I have been through a lot of Homeland security training courses with my Emergency Management degree, and they really don't have much of a sense of humor these days. It isn't impossible to do these things, just be very, very careful about how you build it and think about what it would look like to someone x-raying the box. Just a FYI.

    6 replies

    Reply 1 year ago

    Well Done, But anything with batteries and wires would be suspect...


    Reply 3 years ago

    Ditto. That was my first thought. Remember the kid that built a clock?


    Reply 3 years ago

    ...except the kid who built a clock was fishing for a litigious incident with the guidance of his elders.

    Having gone through TSA training on x-ray identification, a person would have to be in quite a hurry to inadvertently identify any of these components (separate or assembled) as a threat.


    Reply 3 years ago

    or the people who called the cops were just being a bit prejudice/ridiculous/racist/simple.

    If you took a realistic pellet gun on a plane, expect problems. And if youre not smart enough to build this and take it on a plane, you deserve to possibly miss your flight.


    Reply 3 years ago

    So don't put it in your carry on luggage?

    London Lady

    3 years ago

    This is amazing! Though if someone sent this to me and I activated it I would probably just burn the box. ;)


    3 years ago

    Love this. Going to make up a couple, LOL. I have a feeling though the people I will send it to will most likely destroy it instead of looking for a sensible solution.

    Mark AJA

    3 years ago

    The problem with this is that the batteries will run down.

    You could add a solar panel to recharge it !


    3 years ago

    lol are you entering into make a box contest? (if its still open : ) )


    3 years ago

    did pretty much the same thing, with a push button and led display and a flash charging circuit quite a few years ago. with the led display, reading "Do not push button". and if anyone pushed the button, the flash strobe charger would make that whinning noise and the led display read "Release to detonate!". but today you! might just get in trouble with doing something like that.


    3 years ago

    This reminds me of another prankbox . It was a "shocking"nudes photoalbum. Outside there was a picture of a lady in a teetsee bikini. Inside a simple contact batteries and a modified buzzer. The buzzer had a thin wire overwinding that developed a high voltage that was connected to metal strips. The high voltage from the overwinding give the opener a nasty shock. Had a lot of fun with this gadget

    robot bx-31

    3 years ago

    So you're saying that if you turned the key you cannot turn it off?


    3 years ago

    Made one of these when I was Im 55, The only difference is I didnt use a relay , I used a SCR, c106D...with only 3 pins, probibly cheaper and easier to wire up than a relay..and less power consumption.