Trapped Christmas Presents

For over a decade my friend Jay and I have exchange trapped presents at Christmas. When I say trapped I mean it in the classic Circle of Death game style — if you open the present carelessly a buzzer will sound or explosive cap will trigger. It all started when we were designing traps for live-action role-playing games, but quickly became a challenge to one-up each other each year. These days we open all the other presents first and then settle down with our flashlights, dentist tools and wire clippers to work on opening each other’s presents while the rest of the family eats pie and enjoy themselves making unhelpful comments.

Jay and I each have our own style of trap-making. Jay has become a master of secreting traps in places that you’d think he couldn’t access. His high-point is probably the time he gave me a deck of gaming cards that he had somehow unsealed, hollowed out, rigged with a cap-popper trap, then resealed and reshrinkwrapped such that it looked like new again. (That’s rivaled by two years ago, when he managed to plant an explosive inside a cut-then-resealed chocolate egg.) I’m always trying a new angle on things — my favorite is still the time I gave him a “special” version of Looking Glass’ PC game System Shock, which included a specially-included candy red button in the second room of the game that when pressed would berate him for not checking closely for traps as it dropped powerful monsters on his head. (It always helps to know the programmers…)

This past Christmas I wanted to try a trap where the mechanism was plain to see but a puzzle to disarm. The result is the magnet trap shown bottom left. The metal plates at the bottom are sold in joke shops as Exploding Toilet Seat gags. They’re spring-loaded to lift up and set off a cap, but in this case the magnets attached to the top of the popper are being pressed down by the magnets attached to the top of the lid. On one side is a north-polarity magnet being pushed down by another north-polarity magnet, on the other side is a south-polarity magnet pushed down by another south-polarity magnet. The whole system is quite stable — until you try to turn the lid to open the jar. Then the north and south magnets on the lid switch positions and pull the poppers up, setting off the caps. You can see the whole thing in action by clicking on the picture below. Jay tried using magnets underneath the jar to counteract the ones on the lid, but that wasn’t enough force to fight both the magnets and the mechanical spring. I’ll leave the right way to disarm the trap (and the way I originally set it) as an exercise to the reader (and will probably eventually put it in an update).

Jay had two traps this year — the first was a buzzer trap held down by a Borg Teddy Bear that he had gotten at the Star Trek Experience in Los Vegas. It was rigged so if I moved the bear or pulled the wrong wire first it would go off. Remembering my MacGyver lore, I pulled the red one (or was it black?) and disarmed it. The main trap, however, was the bear itself — he had taken it to a teddy-bear factory and had them sew in a voicebox that played his own message. I didn’t set it off (I learned long ago never to press something from jay that says “press me” on it), but am still impressed. You can see it in action from the other movie linked below.

Magnet trap explained
(Quicktime, 3.1M)
Borg Teddy-bear trap
(Quicktime, 750K)

Update (7/24/05): explanation of how to disarm below the fold.

Honestly, leaving this as a riddle without giving everyone the benefit of being able to play with the trap itself is a little unfair. The key is that the magnets pushing down from the metal lid were not actually glued on, but were just stuck on using their own magnetic force. (They consisted of a magnet stuck to the lid, a bunch of steel nuts to give them the right length, and then another magnet at the end.)

To disarm the trap, you open the lid just a bit, then use a strong magnet to slide the magnet towers back to their original position through the lid. Keep opening it a little and sliding the towers back until the lid can be opened enough to stick a (nonmetallic) chopstick into the jar to hold down the poppers.

To set the trap, just reverse the procedure.