By Allan Robinson Updated Mar 24, 2022
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Commercial burglar alarms are intricate devices that require professional maintenance. However, you can illustrate their fundamental principle with a safe, child‑friendly model. This project uses a battery, a buzzer, and a clothes pin to create a functional burglar alarm that’s perfect for a classroom demonstration or a home tinkering session.
Cut a length of wire that will reach from the battery holder to the buzzer. Strip the insulation from both ends. Connect one end to the negative terminal of the battery holder and the other end to the negative terminal of the buzzer.
Strip the insulation from the ends of two more wire lengths. Run one wire from the positive terminal of the battery holder to a thumb tack. Run the other wire from the positive terminal of the buzzer to a second thumb tack.
Press each thumb tack through the arms of the clothes pin so that the flat ends meet when the pin is closed. Place the battery into its holder; the buzzer should sound unless you keep the clothes pin open.
Wrap electrical tape around all exposed wires to prevent accidental short circuits.
Position the open ends of the clothes pin under a window and close the window as tightly as possible. This will hold the pin open, preventing the thumb tacks from touching and completing the circuit. When the window opens, the pin closes, the thumb tacks touch, and the buzzer sounds.
