DIY Intruder Alarm

Clever Engineering, Tech Wizardry


expose any intruders with this diy alarm! an absolute necessity for any sleuth.

this project takes a little time and a little trouble-shooting. and it is *so* rewarding to set the circuitry in action and see it work!

45 minutes

maker checklist

  • foam core board
  • 3-volt buzzer alarm 
  • AA battery holder with switch
  • 2 AA batteries
  • 4-6 double stick foam squares
  • 1 1/2 inch piece uncoated 24-gauge wire
  • 1 old fashioned clothespin
  • 6 foot length of thin, strong chord
  • scissors, pencil, ruler
  • masking tape
  • 1 bit of cardboard (1×1 inch square)


set up your board


affix battery holder to corner of board with double-stick foam squares. make sure to put the batteries in first, and set it so the switch is facing *up* – turn the switch to OFF while you work.


affix the buzzer in the opposite corner using another square of double-stick tape.


twist together the red exposed wires from the battery holder and the alarm. wrap with a small bit of masking or electrical tape.

wire your clothespin


cut two pieces of wire, 6 inches long.


fold a small paper wedge (here, yellow) to hold the clothespin open while you work.


tape one piece of wire to the top, and wrap it around the top portion many times. do the same on the bottom.


secure both in place again with a bit of tape. IMPORTANT! when it is “closed” the wire-wrapped halves should touch, with no tape in the middle.

finish the circut


position the clothespin on the board so the clasp end is facing out, at the edge, and the free wires point away in either direction.


tape the *bottom* of the clothespin in place so that you can press on the top portion and it still opens and closes.


twist one free wire to the black lead of the battery holder and wrap with tape.

test it out


turn the switch on the batter to ON… the alarm should sound!


if it doesn’t sound – TROUBLESHOOT! make sure your connections are strong and secure, and that the wires wrapped around the top and bottom half of the clothespin touch without interference. check your batteries; test your alarm.

do some detective work to find the trouble spot, and then you can fix it!

set the trap


cut a 1-inch square of thin cardboard and punch a small hole near one edge.


tie a 4- to 6-foot length of thin cord through the hole in the cardboard.


set the cardboard square *between* clothespin clasp so the wires on top and bottom don’t touch (it BREAKS the circuit).


set the alarm behind a door and tie the other end of the string in a “trip” position. you may have to tape the board down.