Developer builds a sound locator with Claude Code to find a hidden beeping box

After moving house, developer Simon Willison kept hearing short electronic beeps from boxes in his storage room. The long gaps between beeps made it hard to find by ear. So he used the AI coding tool Claude Code to build Beep Locator, a system that can narrow a sound down to about 40 centimeters.

The system lets five phones, tablets, and computers pick up sound through their microphones via a web page. It finds the source by comparing when the same sound reaches each device. Since auto-detecting device positions wasn't accurate enough, he added a way to drag icons on a map to mark each device.

The program uses Fast Fourier Transform to pick the target beep out of background noise, and syncs all recordings with a short sound from one device. It can even suggest where to place new devices to shrink the search area.

Following the results, Willison checked the boxes and found the source: an old carbon monoxide detector. The project code is now public on GitHub.