Locate a beeping device by triangulating sound across phones and laptops

Something in Willison's box room beeped now and then, too rarely to find by ear. Starting from an empty GitHub repository on his phone, he asked Claude Code to write up the problem: several devices around the room listening at once, a Python web app coordinating them over WebSockets, and ideally the devices locating each other by sound. Claude found a 2007 acoustic ranging paper and wrote the plan into a problem file, then built most of the system, including a way for the server to push new code to listeners without reloading them. On his laptop, Claude Code then ran the server, watched the audio logs and changed the code live while Willison asked for features: a rough mode for dragging devices on the map, a clap test, timestamps, replay of each recording, a button to mark the mystery beep and a repositioning flow. Two iPads, a phone, a MacBook Pro and a Surface acted as listeners.

The devices placing themselves by playing sounds to each other did not work well, so manual rough placement was added and then refined by sound. Clapping around the room gave him confidence the location was right. Once the beep was marked, the system narrowed its position to within about 40cm. In that pile of boxes he found an old carbon monoxide detector with a dying battery. After the first build he mostly sat chatting with the agent while it worked.

The live code push means the server can run arbitrary code on every connected device, which is what saved him from granting microphone permission again on each reload, but it is not something to leave exposed. Claude has no audio input of its own here; it hears only through the scripts it writes. The work moved between Opus 5.5 on the cloud version and Fable 5.2 on the laptop.