Lunchbox alarms can make your kid’s life easier if she has experienced unfortunate events at school, such as finding out that her lunch is no longer in her lunchbox when she takes her break. Lunchbox alarms are a fun way to ensure that your lunch will be there when you look for it. Although creating a trip alarm seems to be difficult, any kid who knows a little about electronics can make one.
You'll need a piece of cardboard or plywood, or even a thin hardbound book big enough to act as a platform for the parts of your alarm. Ideally, your platform would be inconspicuous, and would hide the alarm's components from people who peek into your cubbyhole. You'll also need a 1.5 V battery, a 1.5 V buzzer, a spring-type clothes pin, four lengths of insulated wire with their ends exposed, some nylon thread or kite string, electrical tape, and super glue.
All alarms require three main components: a buzzer, a battery and a switch. The buzzer's job is to generate a loud noise when the alarm trips. The battery acts as the power source for the buzzer. The switch is rigged in such a way that when someone carries your lunch away, the buzzer sounds. These three components are connected in a single circuit powered by the battery and opened or closed by the switch. Before building your alarm, make sure that the buzzer is working and is loud enough for you to hear from a reasonable distance.
Building the Alarm
First, glue or tape the battery and buzzer onto your platform. Using one length of wire, connect the battery's positive terminal to the buzzer's negative terminal. Secure the connections using electrical tape. Take two more lengths of wire and connect one end of each to the free terminals on the buzzer and the battery. Next, wrap each of the free ends of these two wires around the clamping end of the clothes pin. This must be done in such a way that when you pinch the clothes pin open, the exposed wires separate, and when you release the pin, they come into contact. The buzzer should sound when the clothes pin clamps shut. Insert a small piece of cardboard between the wires to silence the buzzer while you glue the clothes pin onto the platform. The switch should be positioned near one edge of the platform.
How It Works
Install your alarm in your cubbyhole with the platform upright and its bottom facing the opening of your cubbyhole. Leave enough space to fit your hand in at the edge where the switch is positioned. Using the kite string, tie a small nonconductive (cardboard, plastic, or rubber) tag onto the handle of your lunchbox. Set up the alarm by pinching the switch open, inserting the tag, and clamping the switch shut. When someone tries to take your lunch, the tag is released and the circuit completed. To remove your lunch box without tripping the buzzer, pinch the switch open and replace the tied-on tag with another piece of nonconductive material.