[other traps]

Under Glass

With most of our traps, half the challenge is finding the trigger before you accidentally set it off. This trap goes the other direction: sliding back the box lid reveals a snugly-fitting glass dome, under which sit two armed poppers (called Bingo Shooting Devices in the novelty biz). The trap's workings are fully visible and it's perfectly safe so long as the glass dome is kept in place, but because the dome is a nearly perfect fit for the box it's nearly impossible to remove the lid far enough to allow access the poppers without them going off first.

When people ask me how to disarm a trap I'm giving Jay I'll often joke that "I just design them, disarming them is his problem," but in reality I like to know that I can get through it before I hand it off to Jay. This one almost had me stumped, because there isn't enough room for the usual tricks of the trade to work. In the end I discovered two different techniques to disarm this style trap, though I confess at the last minute I made a minor design change that made it even more difficult than the version I had disarmed.

Equipment

The key to this trap is finding the right combination of box and glass dome such that the dome fits perfectly into the box. I found both at thrift stores over a period of a few months: the box was a wooden one with a round hole designed to hold drink coasters, the dome is a round glass bowl designed to be an ashtray or small candy bowl.

• Box. Shape and size doesn't matter so long as it matches the shape and size of the dome, though small is preferable.
• Glass dome, bowl or ashtray that fits perfectly inside the box. It should slide easily into the box but not need forcing. This is the tricky part; it took me about three months of rummaging thrift stores to find a box and bowl that fit so well together.
• One or more spring-loaded Bingo Shooting Devices. You can get these in joke shops under a variety of names, but I've found the ones that come in Exploding Pens seem to be of higher quality.
• Percussion Caps
• Double-sided tape
• Flash paper (optional). Also available at joke and magic shops.
• Playing card (optional)

Construction

There are lots of variations you can try with this trap design. You can use one or multiple poppers, attach the poppers to the inside of the box or to the dome itself, stack several poppers together, allow the poppers to move freely or tape them down, and so forth. Different designs will make the trap harder or easier to disarm (and for that matter, to set), and your choice of box and dome will also constrain your design.

For my initial design I had a single popper taped to the underside of the dome, and covered the felt bottom of the box with a cut-down playing card so the popper wouldn't catch and twist when the dome was rotated. The trap worked well, but I was having trouble with some of my caps being duds. For my final design I used two poppers instead of one to insure against duds, and attached them to the playing card itself rather than to the dome because I liked the aesthetics better.

Arming

Arming consists of setting and loading the popper(s) and then holding them down with a strip of stiff paper or cardboard while lowering the dome. Once the dome is in place, you can slide the cardboard out through the side. (If only disarming was that easy!)

For a more dramatic effect, you can sandwich a small sheet of flash paper between the cap and the firing pin. The paper will be held in place by the cap, and will be set off by the cap. The bang will be a bit more muffled than with just the cap, but with more fire.

Disarming

There are several potential methods to disarm this kind of trap, though depending on the particular trap implementation some of them may be more or less effective. I've only actually used the first two methods, the others are suggestions I've heard that sound plausible but haven't been field-tested. Note that there are various destructive methods you could use to open this trap without setting it off, such as drilling a hole from the underside, but that's considered cheating: the idea is to get the "treasure" out of the box without setting off the trap and without damaging either the box or trap itself.

• Strong Magnet: Depending on the strength and position of the popper, placing a strong magnet against the glass (or box bottom) can keep it in closed position while you remove the dome. My earlier prototype with the popper stuck to the glass could be disarmed by simply placing a very strong rare earth magnet against the glass, and then whacking the box, dome and magnet down on the arm of the couch so that the popper would snap shut from the inertia. Once the popper was closed, the magnet was strong enough to keep it closed such that the dome, magnet and popper could all be removed without setting off the cap. (Unfortunately for Jay, the version I gave him was simply too powerful even for the four large rare earth magnets I had brought with me.)

• Rice: The second option is to fill the dome with a substance that can fit through the small crack between the box and glass but still interfere with the firing mechanism. I used grains of rice, which could be forced under the dome using a thin piece of spring steel. After I had a decent amount of rice inside the dome itself I was able to lift it out of the box without firing the cap. The hammer sprung down, but wound up with a single grain of rice between it and the unfired cap. Water would also probably work, though it might damage the box or contents. Note that evacuating the dome of oxygen (for example by using a wine preserver gas) does not seem to work — I'm guessing the caps provide their own oxygen source.

• Wax / glue: We haven't tried this, but it might be possible to carefully maneuver some sticky wax or glue through the crack in the side such that it holds the playing card to the underside of the glass dome, thus pulling the card up with the dome when it's removed from the box.

• Flexible shim: We haven't tried this yet either, but there exist metal shims that are extremely flexible, and such a shim might be able to actually bend through a crack between the glass and box side and get inside enough to block a popper from firing. This was essentially Jay's strategy using pipe cleaners, but they weren't quite flexible enough, and one of the poppers got free and went off.