Claude Code-built Beep Locator finds mystery beep within 40cm

The story begins with a room full of cardboard boxes left unpacked after a move. From around late October 2026, an electronic beep started sounding somewhere in that room at long, irregular intervals, making it hard to pinpoint by ear.

Willison turned to Claude Code and built Beep Locator, which uses microphones on five devices and compares the arrival times of the sound to estimate its origin. He also added a way to mark each device's rough position on a map after an automatic positioning attempt proved insufficiently accurate, and used a fast Fourier transform to pick the target beep out of background noise.

The tool narrowed the source to about a 40cm area. When Willison checked the boxes at that spot, he found an old carbon monoxide detector beeping to ask for a battery change. He noted that the exercise demonstrated giving Claude Code "ears," and the source code is available on GitHub.