Making Your Own Alarm

An alarm, at its most basic, sounds off when electricity from a power source completes a circuit going from the power to a noise-making device -- for example, an electric-powered bell. A homemade security alarm can be made to sound off if anyone steps on a mat placed in front of a door, for instance. You will need supplies from a hobby store and a few household tools, as well as some competency in using a soldering iron. If a child wants to try this project, adult supervision is a must.

4 12-gauge electric wires, 14 inches long
Ruler
Wire strippers
Soldering iron
Solder
Battery pack
Electric-powered bell
2 copper strips, 1-by-2-inches
Mat
Batteries

Instructions

- 1
  Strip ½ inch of insulation off the ends of each wire, using wire strippers.
- 2
  Place the soldering iron on a work surface and plug its power cord into an AC outlet. Heat up the soldering iron for 6 minutes. Place the battery pack, electric-powered bell and the two copper strips on the work surface.
- 3
  Solder an end of one wire to the "Plus" (+) labeled contact on the battery pack. Let 1 minute pass. Solder the other end of the wire to the "Plus" (+) labeled contact on the bell. Let 1 minute pass.
- 4
  Solder an end of another wire to the "Minus" (-) labeled contact on the bell. Let 1 minute pass. Solder the other end of the wire to one side of one of the contact strips. Let 1 minute pass.
- 5
  Solder the end of another wire to the "Minus" (-) labeled contact on the battery pack. Let 1 minute pass. Solder the other end of the wire to one side of the other contact strip. Let 1 minute pass. Unplug the soldering iron.
- 6
  Place the floor mat on the work surface. Make sure you use a floor mat with a bit of a ridge on the bottom that prevents the bottom of the mat from touching the floor. Apply adhesive to one side of the copper strip attached to the bell. Place the copper strip, adhesive side down, onto the center of the mat. Press down on the strip and hold it against the mat for 2 minutes before letting go. Let the adhesive set for 3 hours before continuing.
- 7
  Place the battery pack and bell on the floor, to the side of the door frame. Place the other contact strip, which is connected to the "Minus" (-) labeled contact on the battery pack, on the floor in front of the door.
- 8
  Place the mat, contact strip down, on the floor over the mat. Lie on the floor so that you can see beneath the mat. Position the mat as necessary so that the contact strip on the bottom of the mat is over the contact strip on the floor.
- 9
  Insert the batteries into the battery pack. Try out your alarm by pressing your foot against the mat. This forces the contact strip on the bottom of the mat against the contact strip on the floor to complete the electrical circuit and make the bell sound.

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