How to Build a Lunchbox Alarm

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Build a Lunchbox Alarm
Build a Lunchbox Alarm (Image: Photo by Klikk@dreamstime.com)

Lunch time! It's time to enjoy that ham-and-cheese sandwich you packed in your lunchbox. You pick up your lunchbox--but it feels light. Upon opening it, you discover that once again you've been robbed. Your delicious ham and cheese on wheat is being enjoyed by some thief--again. If only lunchboxes came with alarms. Unfortunately, they don't, but why not make your own?

Things You'll Need

  • Magnetic window switch
  • 9-volt battery
  • Battery holder and clip
  • Piezo buzzer
  • 5-minute epoxy or double-sided tape

Attach the magnetic switch to the lunch box with epoxy or double-sided tape. (The switch listed in the Resources section comes with an adhesive.) Attach the bottom of the switch to the box portion of the lunchbox. Attach the other half of the switch to the lid, directly over the bottom half. They do not need to make contact with each other; a slight gap between the two switch halves is fine.

Adhere the piezo buzzer to the side of the box, using 5 minute epoxy or double-sided tape. To minimize wire length, mount the buzzer close to the magnetic switch.

Mount the battery holder close to the buzzer and switch. The battery holder listed in the Resources section can be mounted with a small screw, a pop rivet or double-sided tape.

Connect one lead from the piezo buzzer to the COM terminal of the magnetic switch. Make the connection by clamping the stripped end of the wire lead under the COM terminal screw.

Connect the other piezo buzzer lead to the red lead of the battery clip. Connect the black lead of the battery clip to the NO terminal of the switch.

Install the 9-volt battery in the holder and connect the clip to it. The alarm will sound at this point because the box is open.

Tips & Warnings

  • To keep the alarm from staying on when you open the box, place a small magnet on top of the bottom (wired) half of the switch. Remove this magnet when you close the lid to arm the alarm.
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