Introduction: Sonic Tripwire Alarm

Picture of Sonic Tripwire Alarm

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:

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Start by removing the battery from the alarm clock.

Step 3:

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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:

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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:

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

Step 6:

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

Step 7:

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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:

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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:

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

Step 10:

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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:

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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:

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

Step 13:

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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:

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

Step 15:

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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!


Errol1951 (author)2015-11-28

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

hertzclone made it! (author)2015-11-06

I used your idea but made some changes, I had a couple of buzzers that were part of a previous project and no longer being used, I fastened one the the cover of a small project box I purchased at Radio Shack. I had a 9 volt battery bracket and mounted it inside the box, I installed a socket for a phono plug jack on one end so we could use it if we wanted a remote trip trigger away from where we would place the alarm box. I used wooden clothes pin clips as the trigger, I went fancy and installed #8 flush head screws through the clamp end of the clothers pin as the contacts. I used pop rivets to mount the clothes pin to the edge of the box, drilled a couple of small holes in the box to get the wires from the trigger inside the box. I used heat shrink tubing to secure the wire to the top jaw of the clothes pin. For the remote trigger I made a duplicate of the box mounted clothes pin but added about 6 feet of wire that ended with a male phono jack. I used some split wire sleeving that I had on hand to cover and keep the wires from getting tangled. I have since painted the clothes pins black, added a spike to the box to allow it to be stuck in the ground, and a velcro strap to the remote trigger to allow it to be mounted to something. This was a fun project for my son and I, we has used it in some of the air soft battles he has had with his friends.

This looks awesome! So much better than my concept. I'm glad my idea inspired you to make that! I can see where you've made changes. 9v battery will last a whole lot longer and the project box is easier to weatherproof. Hat off to you sir!

Thank you very much for the compliments. You provided a great base from which I started, the concpet was not something that I had thought of. My son thinks this is the greatest thing, he had friends over yesterday and when the battle was over several of his friends wanted to know if I could make additional ones for them.

RBot_2000 (author)2015-10-20

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!

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

Lt.Greg (author)2015-10-20

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"!

MadScienceHacks (author)Lt.Greg2015-10-28

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!

C3idotnet (author)2015-10-21

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...

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

manutea (author)2015-10-20

cool project

MadScienceHacks (author)manutea2015-10-28

Thank you!

Alex 2Q (author)2015-10-24

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 ;)

MadScienceHacks (author)Alex 2Q2015-10-28

Thank you so much! Glad you like it!

ck0050 (author)2015-10-20


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

MadScienceHacks (author)ck00502015-10-28

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

zappenfusen (author)2015-10-20


Aebleskivers (author)zappenfusen2015-10-20

Running shoes - cross trainers

zappenfusen (author)Aebleskivers2015-10-21

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...

Y-Geo (author)2015-10-20


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

MadScienceHacks (author)Y-Geo2015-10-20

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

Y-Geo (author)MadScienceHacks2015-10-20

your welcome :-)

akb (author)2015-10-20

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.

MadScienceHacks (author)akb2015-10-20

That is a great idea! I'm so glad that you found my idea useful!

snosey (author)2015-10-20

This is a great safety device. I'd like to use it on all my windows and doors. Thank you.

MadScienceHacks (author)snosey2015-10-20

This can be modified for that purpose!

IamGutter (author)2015-10-17

Great Instructable. Simple, cheap portable and effective! May have to make one to let me know when my dogs have entered the "forbidden zone" of the pantry! Thanks!

Thanks! Hope you enjoy the build!

Cyberscann54 (author)2015-10-16

cool project but there is nothing sonic about it

BrainLinq (author)Cyberscann542015-10-20


sonic: (adjective) - relating to or using sound waves.

You must be confused.... maybe you are thinking ultrasonic.

That is correct. Everyone has their own opinion of what the word sonic is. Using Sound waves is the correct definition.


IamGutter (author)Cyberscann542015-10-17

While the title lead me to believe there would be sound waves used in the detection of an intruder, which it doesn't, I believe there is absolutely something sonic about this. When an intruder trips the wire this alarm makes a sound; sonic. Just as if the trip wire turned on a light when it was triggered it could accurately be called a visual alarm, not meaning it had to see something before it was tripped but that you could see something which indicated it had been tripped.

MTtoo (author)2015-10-18

Great Instructable. Would be a lot better with more pictures on each step rather than so many steps. Viet Cong in Vietnam used this same idea to detonate unexploded bombs placed along trails.

MadScienceHacks (author)MTtoo2015-10-20

You could always watch the video?

Sarvasv Kulpati (author)2015-10-17

awesome! would you be interested in making a video together on youtube?

Thank you ! Not collaborating at this time.

How about replacing the wire with a ultrasound beam. It really would be sonic, then. You could also use a laser (non-visible variety), if you don't mind living dangerously.

What would be the cost of one of those?

XXENNON9630 (author)2015-10-18

An easier sonic (loud) tripwire would be using green garden tie wire in a roll, 2 , inch square stakes, 1 personal attack alarm with pin pull, put the stakes in the ground tie one end of garden wire to one stake the other end to the pull pin in the alarm, gaffa tape the alarm to the other stake, length of the line as required. I use this in my garden entrance, and across my back garden, they work and scare intruders out their trainers

tonyshope (author)XXENNON96302015-10-20

I use your same idea while camping or out and about, simple lite weight strong wire o the persoanl alarm and BOOM spooky spook.....

Yes! Especially useful in bear country!

florin2901 (author)2015-10-20

Very nice ideea..... It can be used in many more combinations with some nice applications.....

I'd be keen to see what other ideas people come up with. This is free to everyone to change and adjust as needed.

MSawyer (author)2015-10-20

Put an aspirin or sugar cube between contacts and place on the basement floor, flood alarm. Or ice cube in the freezer.

MadScienceHacks (author)MSawyer2015-10-20

Very good! Yes! That might work!

laplante1367. (author)2015-10-20

Great project! How about something for deaf and hard of hearing people. I would

need some kind of light or vibrator(pillow) instead of sound.

jumpfroggy (author)laplante1367.2015-10-20

How about an old-school alarm clock that has the bells on top? There are some battery powered one, and you could probably feel that going off even if you couldn't hear it.

Or you could use the same concept, but instead of a clock w/ alarm, you use what's essentially the vibrating motor from an old cell phone. Very compact, could put that under the pillow.

Yes! Awesome ideas. This is just a concept. Feel free to modify the idea as needed.

One of the guys who commented on my YouTube channel made one with an LED light! I thought it was sooooo brilliant! Instead of connecting wires to a clock, connect it to an LED torch. It should work the same way.

About This Instructable




Bio: 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 ... More »
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