Refrigerator Door Open Alarm

A refrigerator is meant to keep a limited space cold inside your house, and if the door is left ajar – even a tiny bit – its effectiveness is greatly reduced. To keep this from happening on his alarm-less fridge, Lukas K. of carrotIndustries created an add-on fridge buzzer board that tells him when the door has been left open too long.

In operation, a buzzer sounds a low-pitched beep if the door has been open for 90 seconds, switching to a higher-pitched tone at 120 seconds to let you know that it really needs to be shut. Lukas conveniently included a button that can be pushed to manually silence it, perhaps if you’re cleaning, and it also cuts off after five minutes, avoiding long-term annoyance and/or battery drain in case of a malfunction.

The device uses a low-power TI MSP430G2232 MCU for control, and a Silicon Labs Si7201 Hall effect sensor detects the door position via a magnet attached to the fridge cabinet. An inductor is connected in parallel to the piezo buzzer in order to increase its volume. The unit runs on a single CR2032 battery, which should theoretically enable the board to work for around nine years, given its standby current consumption of under 3µA.

Firmware and hardware files are available under an open source license, allowing you to create your own, or build on the design. The board includes six-pin Tag-Connect footprint for programming, and potential future modification.