When you think of perimeter alarms, your brain probably conjures up images of laser beams, loud sirens, and jewel thieves in black ski masks. Such alarm systems certainly exist, and if you’ve got a degree in security technology, you could probably put one together with a few spare laser pointers and a megaphone. But, perimeter alarms don’t have to be high-tech, and you don’t have to be a jewel collector to need one.

Imagine you’re on a camping trip in Alaska during the peak of summer, when plenty of grizzlies are ambling about looking for an easy dinner. A low-tech perimeter alarm can alert you when a wandering cub gets a little too close to your camp. In addition to notifying you of intruders, perimeter alarms also tend to scare off whatever got too close, so you’ve got a warning and a deterrent packaged in one convenient system.

In this example, we’re making a low-tech perimeter alarm out of aluminum cans, a few sticks, paracord, and trip wire. If you don’t carry trip wire in your camping kit, a high test fishing line will work just as well. Bonus points if you get a fishing line that’s a darker color, which helps it blend in with the surroundings. Here’s how to make your own jury-rigged security system. 

Step 1: Place the Alarm

Tie together at least a few aluminum cans with a short length of paracord or wire/fishing line. 

Find a tree with a Y-shaped trunk, or just two trees that are growing close together. Tie a loop around the trunks with paracord.

Attach the cans in the space between the trunks. They should hang freely.

Step 2: Tie Another Loop