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.

DIFFICULTY: MODERATE

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

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 - http://bit.ly/1ODLIwG

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

Start by removing the battery from the alarm clock.

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.

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

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

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

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.

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.

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

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.

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.

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

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

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

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!