in: Manly Know-How, Skills

• Last updated: June 1, 2021

How to Make a Low-Tech Perimeter Alarm

A tin can hang for perimeter alarm.

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

A man holding some empty cans with a sting.Tie together at least a few aluminum cans with a short length of paracord or wire/fishing line. 
Tying together two trees with paracord.

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.

Attaching cans with a wide paracord.

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

Step 2: Tie Another Loop

Second loop of paracord below cans.

Use more paracord to make a second loop below your cans. For now, this one should hang loosely between the trunks.

Step 3: Make the Trigger

Find three sticks of about the same diameter, but different lengths. One should be about the length of your forearm, one should be slightly longer than the space between the trunks, and a final stick should be about the length of your index finger.

Using stick to check the cans alarm.

Take the stick that’s the length of your forearm and place it in the center of the loose loop. Rotate the stick to twist and tighten the loop. The stick should end up just below the cans such that when you rotate the stick, it passes through them.

Stick and cans centered equally.

When the stick is tight in the loop, place the longer stick across the two trunks to hold the vertical stick in place.

Using third stick as a trigger stick.

Take the third, smallest stick, and prop it between the other two sticks. This is your trigger stick.

Step 4: Create Your Perimeter

Paracord is attached to big tree.

Establish your perimeter by choosing a nearby tree and tying your trip wire or fishing line to its base. Run the line back to your can alarm, routing through a root, forked stick, or limb to keep it close to the ground.

A man has paracord in his hand.

Step 5: Set the Alarm

Pull up trigger stick for alarm.

Finally, pull the trip wire taut and tie it to your trigger stick. When someone or something walks through the trip wire, it will release the trigger stick. Once the trigger stick releases, the twisted stick will spin in place and whack against the cans (see video below), giving you and the intruder plenty of time to react.

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