How to Build Burglar Alarms

Burglar alarms can be simple or complex, but all of them are built around three basic components: a bell or alarm, a battery to power it, and a trigger switch. When someone triggers the switch, it completes the circuit (or disconnects the circuit in some cases) and the alarm sounds. You can make a burglar alarm of your own with very simple materials, using this basic formula as a guide.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• 4 pieces of insulated wire at least 1 foot in length Scissors 1.5 volt electric alarm or buzzer 1.5 volt battery Electrical tape or glue Spring-type clothes pin Small piece of cardboard Pin 3 feet of string 1 piece of plywood at least 4 inches by 12 inches

1. Strip the insulation off of the tips of wire. They will be attached to the battery and the buzzer.

2. Connect the end of one wire to the positive (+) terminal of the battery and the end of a second wire to the negative (--) terminal of the battery. Connect the other two wires to the positive and negative terminals of the buzzer.

3. Secure the battery to one end of the plywood and the buzzer to the other side using glue or electrical tape.

4. Wrap the free end of the wire connected to the positive terminal on the battery around one of the two jaws on the clothespin. Wrap the free end of the wire connected to the positive end of the buzzer around the other jaw. The two wires should touch when the clothespin jaws are closed.

5. Poke a hole in the cardboard with a pin and run a piece of string through it. The hole should be closer to one side of the cardboard than the other. Tie the string securely in place.

6. Place the cardboard in between the jaws of the clothespin. It should completely prevent the wires from touching. The string should not be clamped by the jaws at all (you'll want to pull the piece of cardboard out to complete the circuit and set off the alarm).

7. Tape or glue the clothespin to the plywood in between the battery and the buzzer.

8. Connect the wires from the negative terminals of the battery and the buzzer together. You can wrap them in electrical tape to help secure the connection.

9. Tap or glue the plywood to the door or window you want to secure. It should be close to the end of the door or window, where it touches the wall when it closes.

10. Close the door or window and secure the free end of the string to a nearby wall with tape or a pushpin.

11. Test your burglar alarm. When you open the door or window, the cardboard in the clothesline jaws should be jerked out, completing the circuit and setting off the buzzer.

Tips & Warnings

• Make sure the positive and negative terminals of the battery and buzzer line up. You want the positive ends connected to either side of the clothespin jaws and the negative ends connected to each other. Otherwise, the circuit won't work.