You have hiked all day, miles and miles, to the most isolated spot you can find. It’s quiet, beautiful, peaceful, just what you wanted. Being the great lover of the outdoors that you are, you decide to cowboy camp and just toss your pack up against a rock, throw down a blanket, and get some sleep. Many hours later, when you wake up, you realize something isn’t right? Your pack is gone!  You search high and low, nothing. What can you do? 

At that point, nothing. Somebody or something (a bear, maybe?) has walked right up to your camp and run off with all of your supplies. If you had prepared though you could have set up a camping tripwire alarm system. 

A tripwire alarm can scare off both people and animals that might want to intrude on your camp.

How do trip alarms work 

As far as security goes, a tripwire alarm might be as simple and effective as it gets. The simplest DIY versions just involve a string and something to make noise. You stretch the string across a path or even around your campsite. When an intruder trips on the string an alarm goes off to alert you that some person or animal has entered your space. 

The exact setup for a trip wire alarm system can vary and with modern technologies, the traditional tripwire has been updated. Now, a broader definition is needed. Today a DIY tripwire alarm can be set up with almost anything that detects movement through an area and then activates an alarm.      

Classifying trip alarms 

Tripwire alarms can be broadly categorized into three types depending on how they are constructed.

• The classic direct tripwire alarm: This involves a physical line such as string, wire or cord stretched across an area and connected directly to an alarm which is anything that makes a loud noise. When something hits the string and pulls on it, like a leg stepping forward, it triggers a mechanism to set off the alarm. 

• The laser/infrared tripwire alarm: This works just like a classic tripwire but instead of using a physical line like a string you use an invisible laser/infrared beam in its place. A transmitter fires a beam at a receiver which is connected directly to an alarm. If the receiver doesn’t detect the beam, as would happen with an animal walking in front of it, then the alarm is activated. DIY electronics are now so cheap and accessible that this type of do it yourself tripwire alarm is easier to make than you might think. Just check Amazon or even Walmart and you can find most supplies. 

• Radiofrequency tripwire alarm: This trip alarm involves a wireless connection between the tripwire setup and the alarm itself. When either a classic or laser tripwire is tripped a radio transmitter is activated which sends a signal to a receiver on the alarm and turns it on. Although this trip alarm is a more involved DIY project the upside is that you can place alarms far away from the tripwire or even carry an alarm with you.    

Don’t worry if the modern tripwire alarms seem a little too involved. We’ll start by going over how you can make a classic direct tripwire yourself and for most purposes that might be enough. If you feel adventurous in your DIY skills or electronics suit you then we will also cover some of the modern tripwire constructions that you can do.      

The DIY classic direct tripwire alarm 

There are many ways you can build a classic tripwire alarm. Some are very simple and some are complex. For example, you might consider a string, tied between two trees, with several bells on it to be a trip alarm. It would certainly be noisy if someone hit it. Here we will cover two examples that are a little more involved but very effective. 

Example 1: The Air Horn Alarm 

Supplies needed:

• An air horn
• String
• A short sturdy stick
• A heavy flat rock 

Step 1: Find a good spot to set up your alarm. A path with tall grass and trees on both sides would be ideal for this alarm.

Step 2: Bury the air horn in the ground just enough so it is stable but the horn and button are still exposed. 

Step 3: Tie one end of the string to the stick and the other end to something sturdy like a tree or stake.  

Step 4: Prop up the flat rock with the stick so that when the stick is pulled the rock falls on the air horn and activates it. 

Step 5: Make sure the string is about a foot off the ground and stretched tightly across a space where you might expect an intruder.   

With this setup when an intruder hits the string it will pull the stick out from under the rock. This will cause the rock to fall on the airhorn setting it off. You can set up multiples of these or get creative with the construction. For example, tie more than one string to the stick so you have multiple tripwires activating the same alarm. You can also run a string from the stick around your whole campsite to make a perimeter alarm, one tripwire can protect the entire area. 

A simple mousetrap can be adapted to make a great tripwire alarm.

Example 2: The Mousetrap Alarm 

Supplies needed:

• Fishing line 
• Large plastic tent pegs
• A mousetrap
• Screws 
• Small finishing nails
• Ring caps 
• Rubber bands 

This classic trip alarm is a little more involved than the first one but it is too good not to mention. The way it works is when the tripwire is hit it activates the mousetrap which in turn slams down on one of the ring caps. Ring caps are the little plastic pieces that go in toy guns to make them go “Bang!”. This trap will do the same and scare off any intruder. 

Step 1: Find the right spot for your tripwire alarm. This needs to be a place where an intruder is likely to go. This whole thing won’t work if they just walk around the tripwire. A clearing between two trees would be great. 

Step 2: Attach the mousetrap to one of the tent pegs using a couple of screws. 

Step 3: Find the bait peddle on the mousetrap. This is the little piece a mouse would step on to activate the trap. Drill a small hole in the trap behind this piece and pass one end of the fishing line through the hole so you can tie it to the bait peddle. This way, when the string is pulled, it activates the trap.

Step 4: Now you need to find what part of the trap gets hit when you activate it. Where does the bar slam down? Mark two dots on either side of the trap where this happens and then hammer in two nails there until the heads stick out less than a quarter-inch above the trap. 

Step 5: Cut off individual ring caps and stick them on the heads of the nails. 

Step 6: Place the tent peg with the mousetrap and string attached on one side of a clearing and stretch the fishing line across. Tie off the other end of this line to the second tent peg and make sure the line is tight. Now you should have a tripwire set up with one end attached to the bait peddle of the mousetrap and the other tied to a tent peg.

Step 7 (optional): If the fishing line isn’t tight enough grab some rubber bands and wrap them around the bottom half of the mousetrap trapping some of the extra string with it. This should help. 

If everything is set up correctly then when someone hits the tripwire it will pull on the bait peddle in the mousetrap and set it off. This will cause the bar to slam down on the nail heads with the ring caps and the whole thing will go off with a bang! Once you have this built you can easily pack it and set it up anywhere. Also, to make the tripwire less conspicuous you should spray paint the whole thing a dark green, brown, or black to help it blend in with the surroundings. So now we have covered two DIY classic tripwire alarm projects. You can definitely get creative with this type of tripwire.  

The DIY laser tripwire alarm 

Note: Making a laser tripwire alarm requires some experience with electronics and soldering, or the willingness to learn. If you’re new to this kind of thing it might seem daunting at first, stick with it though and you will have a working tripwire alarm in no time. 

With modern technology, the classic tripwire alarm has slowly evolved into something with fewer and fewer moving parts. With a little bit of electronics know-how and a laser, you can make a tripwire alarm that is very effective. 

Take note, classic tripwire alarms are the simplest and most versatile for camping. You don’t have to worry about electronics or weatherproofing. Still, for people who camp in a vehicle like an RV the electronic and cordless tripwires can be very useful. You can set this up in windows and doorways without ever having to take it down. Like with most security systems, you just turn on the system and go. 

Supplies needed: 

• Laser pointer
• A printed circuit board 
• 555 Timer IC
• 3-12 volt buzzer 
• Switch
• CdS photoresistor 
• 2 resistors 
• 3 AA batteries 
• A 3 AA battery holder 
• Jumper wires 
• Heat shrink tubing 
• Mirrors (optional) 
• Soldering gun 
• Glue gun 
• Multimeter

This tripwire alarm is clearly a lot more work but the final product is also a lot more effective than a classic tripwire alarm. The way this type of alarm works is a sensor detects a laser beam and when the laser is interrupted the sensor sets off an alarm. In this case, the sensor that detects the laser is the CdS photoresistor. This photoresistor is hooked up in such a way that when the laser is interrupted it causes a shift in the voltage of the system and the buzzer goes off. 

Safety note: Never point a laser at someone’s eyes or at passing aircraft. This can be very dangerous. It is also a good idea to wear eye protection when working with lasers.  

Step 1: Connect your CdS photoresistor to a multimeter and then shine the laser pointer at it. With this light on the resistor check the resistance of the photoresistor. This number can vary but you need to know it to find out what resistors you need. For this example let’s assume the resistance is 100 ohms. That means you will need 100-ohm resistors. 

Step 2: Now, you are going to have to spend some time with this diagram:

This is how the tripwire alarm works and this is how you are going to put it together. To make the whole thing simpler the big box in the middle is your piece called a 555 timer IC. It will come with instructions that tell you which pins correspond with which numbers.  

As mentioned, this DIY project is most appropriate for people with electronics knowledge. But, as a review, every black line on that diagram is a connection between the parts of your alarm. The numbers represent pins, or attachment points, where you will be soldering wires. 

• CdS Photoresistor: this is the big circle with the zigzag line through it 
• Resistors: these are the zig-zag lines by themselves 
• 555 timer IC: this is the big rectangle labeled with 1, 2, 3, 4, 6, and 8
• 3-13 volt buzzer: this is the image that looks like a speaker
• Switch: This is gap below the buzzer where you see the (-) negative sign and the 3 
• Battery pack with 3 AA batteries: VCC and GND are the two ends of the battery pack. 

Step 3: Solder everything together on the printed circuit board. Use the glue gun and some rubber bands to hold any loose components together.

Step 4: Set everything up. First, you can attach the laser pointer somewhere with some sticky tack or glue and use some duct tape to help hold the button down. Once the laser pointer is secure you can then attach the alarm you built and line up the photoresistor with the laser. When it is ready to go just flip the switch and test it out!  

Step 5 (optional): Use mirrors! This is one of the things that make a laser tripwire so worth it! Using mirrors you can bounce a single laser beam around a large area and back onto the photoresistor for full perimeter security. That way when someone enters any part of the room they set off the alarm. This can work in RV’s and large tents too. 

Step 6 (optional): Put your alarm and laser pointer inside a weatherproof casing for outdoor use.          

You can harness radio frequencies to expand the range of your tripwire alarm.

The DIY radiofrequency tripwire alarm 

You can take your tripwire alarm to the next level by integrating radiofrequency alarm activation. If that interests you then check out this tutorial from one of the Make community engineers which makes use of an old doorbell. You can also find great video tutorials on the subject with other high tech and low tech modifications. As you expand your tech knowledge you can even include other security measures like a motion sensor or cameras.   

How to conceal your tripwire alarm 

The only thing worse than someone stepping around your tripwire alarm is them seeing it and just stepping right over it. During the construction and setup of your alarm, there are some things you can do to help conceal it. 

1. Use natural colors: As much as possible you should use parts that match the colors of nature. For example, you can buy a green monofilament for your tripwire. If something is the wrong color then go ahead and paint it. With tripwires that use a laser or any kind of visual receiver-transmitter be careful not to paint over that part.

2. Use nature: Use tall grass, bushes, logs, trees, underbrush and whatever else you find to help conceal your tripwire. Place branches and other distracting things at eye level so someone walking along will be more focused on that than the ground. 

3. Use other distractions: Get creative with distractions. Signs, colors, sounds and more can all help distract a would-be intruder or burglar from the tripwire you have set. 

4. Misdirection and deception: It might not be the first tripwire that catches an intruder but the second. The more tripwires you set up the greater the chance is that someone will trip one. An intruder that sees the first tripwire might not expect another one after that.     

Why build a tripwire alarm while camping?

Tripwire alarms are for people and animals. If you are a prepper, survivalist, avid camper or even just like to play paintball then knowing how to make one is useful. The noise alone can scare off most intruders and will, at the very least, alert you when needed. 

Camping makes you vulnerable to opportunistic thieves, including hungry animals looking to pilfer your food. The further you are away from a resupply point the more important it becomes to protect whatever supplies you have. This is why a tripwire alarm can be so useful. It is a security policy for your safety.

With a good tripwire system in place, you can rest easy at your campsite.

Final Verdict:

A tripwire alarm can be as simple or as complex as you want to make it and the different approaches each have their pros and cons. Classic tripwires are easier to construct and tougher outdoors but are limited in their reach. More modern constructions are better for permanent installation and can activate alarms at greater distances, but their downside is the need to weatherproof the electronics for outdoor use.

When you are camping a tripwire can bring you much-needed peace of mind and a sense of security. Many tent campers use classic tripwire constructions while RV campers might benefit more from laser tripwires. Radiofrequency alarm activation can be useful in both cases. Ultimately you have to try out different systems and find what works best for you. With time it just might become an essential part of your survival gear. 

Bonus tip: Check out these loud and effective camping trip alarms which take advantage of a custom shotgun like blanks!