[other traps]

Laser

This is a strikingly beautiful trap. When placed in a darkened room, you can see a faint and ominous glow coming from the chest even before testing the latch. Opening the chest reveals faint laser lines criss-crossing back and forth across the mouth of the chest, lines that might be missed completely in a well-lit room but become bright if you blow smoke or mist into the box. Breaking a beam with your hand, or bump one of the carefully-positioned mirrors that bounces it from source to receiver and you trigger an alarm.

Equipment

• Light Sensor + Alarm. Jay used a toy called the Lazer Tripwire from SpyGear which has a good interface and simple all-in-one package (you only need one of the three units, though you can also use all three as originally designed). You can also build your own circuit that triggers a buzzer whenever a light sensor goes dark.
• Chest. Anything more than a foot or two across will work. Jay used a nice wicker chest, which has the added advantage of letting enough light through the slats that you can see an ominous glow coming from inside before you even start opening it.
• Laser pointer. I personally like the green laser pointers, but the cheap-o red laser pointers work fine as well (though possibly with fewer bounces before they're no longer bright enough). You'll want one that has an on-off switch rather than a press-and-hold button.
• Small mirrors, about an inch on a side. You can get these at any good craft store.
• Modeling clay. Also at craft stores.

Construction

Start by turning on your laser pointer and tacking it in a corner of the chest with a dab of modeling clay. Then place a dab of clay where the beam hits the chest wall and stick a mirror to it such that the beam bounces back across the chest. Keep adding mirrors until the laser has criss-crossed the chest several times. Depending on the strength of your laser and sensitivity of your light sensor you should be able to get between 3-5 crossings, maybe more. You can use the modeling clay to fine-tune your mirror placement, aiming the beam both vertically and horizontally across the chest. Your last beam should land on your light sensor.

You can do many things to make this trap harder or easier to disarm. Beams which cover the space without any large dead-zones make it harder, as does changing the height of different beams (essentially changing the security grid from a 2D puzzle into a 3D one). You can also bounce a beam over the light sensor before bouncing it back to land directly on it: that makes it harder for your would-be MacGyver to reach the on-off button or battery clip without tripping the alarm. For an extra challenge, you can add obstacles that don't block the beams but do block someone else's beams, tools or line of sight. Or you could be a real bastard and attach one of your mirrors to the lid of the chest itself, but even I wouldn't be that cruel...

Finally, if you want you can daisy-chain several light sensor / laser pairs in a row. When the master light sensor goes dark it trips the alarm. When any other light sensor goes dark it simply turns off the laser pointer it's paired with, which then cascades back to the master. This is how the Lazer Tripwire toy works. The set-up takes more space, but it has the advantage of allowing you to use more (or weaker) beams, and means anyone who disables one of the slave sensors before disabling the master will trigger the alarm. (Of course, you could also equip all three sensors with alarms, making the guessing game moot.)

Arming

The Lazer Tripwire toy makes arming simple: just turn on your laser pointer (correcting any mirrors that might have gotten bumped in the process) and then turn on the sensor. Once your beam has stayed on the sensor's target pad for a few seconds an appropriately sexy British voice will say "System Armed," and that's all there is.

Disarming

Jay suggests three different ways to disarm this trap. In all three cases the first thing you'll want to do is turn out the room lights and then spritz a mister (or perfume atomizer if you don't mind the smell) into the chest so you can see the beams.

1. Contortions: The straightforward approach. Once you know where the beams are, just carefully reach in and contort your arm, tweezers or other tools until you can get your booty out of the chest without interrupting any of the beams. Probably ranks a C+ for strategy, but gets an A for dramatic tension. This is what I did, but then I always did like dramatic tension.

2. Disable the sensor: If you can identify and reach the off switch or battery compartment of the light sensor without triggering the trap then you can simply switch it off. If you're dealing with a daisy-chained set of sensors with a single master then you're taking a chance: pick the wrong one and you'll simply set off the alarm. Jay helpfully made sure to leave the logo on the sensors visible in case I thought to do a Google search for their schematics.

3. Provide your own light: By far the most stylish method is to shine your own laser pointer directly into the light sensor, and then you can break the other beams at will. (You do have a laser pointer in your trap disarming kit, don't you?) Of course, if there are multiple sensors then you'll only disable some of the beams this way, but that should be enough. (I hear that real light-beam security systems actually send encoded information via the beam so this trick won't work, but it still wins major style points in my book.)