Sonic Tripwire Alarm





Introduction: Sonic Tripwire Alarm

About: I am a photographer and ex-Engineering Student with more than just a curious mind. I use my knowledge about photography and basic engineering to create stunning videos for my YouTube channel (madsciencehacks...

In this Instructable, I'll show you how to make a simple sonic tripwire alarm that you can use at airsoft games or as an early-warning system for preppers.


Here's what you'll need : -

  • A cheap alarm clock that beeps, just like this one (see picture above or video below).
  • Braided fishing line, nylon fishing line or upholstery thread.
  • An old credit card or gift card.
  • A short length of thin electrical wire.
  • A piece of tin foil
  • Electrical tape
  • A clothes peg made of plastic or wood.
  • And an allen key

Other items required :-

  • Scissors
  • Knife
  • Wire strippers
  • Hot Glue gun and glue sticks
  • Straight Edge
  • Paint of choice
  • Zip ties, rope or a clamp
  • AA battery

Step 1: Watch the Video! *Required*

It is essential that you watch the video above to hear and see how this concept works. You will also need to hear the alarm beep to ensure you source the correct alarm clock for this build. If you cannot see the video above, find it on my YouTube channel by clicking here -

Once you watch the video, head over to step two!

Step 2:

Start by removing the battery from the alarm clock.

Step 3:

Then strip the ends of the electrical wire on one side and then join one wire to the spring side of the battery holder just like this.

Step 4:

Attach the other stripped end to the negative side of the battery using some electrical tape and insert the battery back into the clock

Step 5:

Strip the other ends of the electrical wire and touch them together to complete the circuit.

Step 6:

Then replace the back cover on the clock just to make everything look a bit tidy.

Step 7:

Next, Cut two half inch by one and a half inch strips of tin foil and glue them onto the jaws of the clothes peg. This will form the tripwire switch.

Step 8:

Position one end of the electrical wire onto each strip of tin foil. The alarm should beep when the jaws are closed and stop beeping when the jaws are open.

Than glue the wires in place with some hot glue and then test the switch by opening and closing the peg.

Step 9:

Glue the peg onto the body of the clock using some hot glue just like this.

Step 10:

Then glue on the allen key to the bottom of the clock to allow the tripwire to be mounted anywhere using cable ties, clamps or rope.

Step 11:

Now you can paint it to make it look a bit more inconspicuous. Just remember to leave the window unpainted so you can set the alarm later.

Step 12:

Next, punch a hole in the credit card and cut out a piece with the hole just like this.

Step 13:

Thread the fishing line through the hole and tie it securely and then slide piece of credit card between the jaws of the peg.

Step 14:

Switch the alarm on and then tug on the fishing line to make sure the switch works.

Step 15:

To demonstrate this concept, I mounted the tripwire between two chair legs and use my hand to trip the alarm.

You can use this concept and design your tripwire according to your specific needs. Improve on this idea and make it even more effective.

Please watch the video to hear how it sounds!



  • Planter Challenge

    Planter Challenge
  • Make it Move Contest

    Make it Move Contest
  • Woodworking Contest

    Woodworking Contest

We have a be nice policy.
Please be positive and constructive.




Great idea I have been thinking about using cheap personal alarms with the pull pin to trigger just use some fishing line and when someone walks through they wouldn't even know they had triggered it

If you don't have an alarm clock, and don't want to get one, you can just use a simple buzzer for a high pitch sound. Cool project!

1 reply

Someone mentioned the use of a tactial (personal protection) alarm. I also thought about using the alarm fishermen use when fishing for carp.

Nice idea! I've done it different ways as an alarm for my campsites. Its great to see people who still know how to "Improvise, Adapt and Overcome"!

1 reply

I'm still learning how to be resourceful. I've made it a habit to find ways to use regular household items to do something amazing that it was not designed to do. This for example or any of my other instructables .

Thanks for your support!

Thx for posting this. For those interested u could easily add the visual aid or vibrator by utilizing an led along with whatever sonic implementation u want. Substitute the clock for a D cell or AA battery holder using the credit card shard as the insulator. Very simple and quick. Even waterproof it if u want with duct tape or other...

1 reply

Thank you! I really like your waterproof/weatherproof idea.

Hi cool project. This reminds me of some IED training devices I built a few years ago. Thanks for the inspiration as I got some ideas for my own version.

Cheers Alex

PS: You got a new follower and subscriber on your YouTube channel ;)

1 reply


instead of making that clothes pegs trigger, you can simply slip that credit card thing between the battery and the contact on the clock.

1 reply

Your suggested method might pull out the battery if the wire is tripped.

Gotcha! Ignorance is bliss on that subject.... For me at least. All of my Cross Training consisted of climbing various height ladders. 6', 8', extension...


if you have wooden clothes pegs you can use to brass thumb tacks as the contacts , have used button headed machine screws and "earth" wire eyelets from the auto store as well in a similar trigger device

2 replies

Nice! That will eliminate the need for Glue and foil!

your welcome :-)


Excellent Instructable. Such a simple idea but so easy. I'm going to build one of these but instead of an alarm clock I'm going to use a small piezo buzzer. I can buy one for under $2 and it is extremely loud. I plan to use it when I stay in hotels by putting it across the door. If anyone comes in it should wake me and hopefully scare off the intruder. It should also make the whole unit much more compact.