Build a Home Assistant screen for a rooted Nest Learning Thermostat

The poster, u/sysmoon, had an older Nest Learning Thermostat that Google no longer supports. Another project, unfr0zen, had already worked out how to root these units over USB, cut them off from Google and run them locally. The poster forked it and had Claude Code build the parts on top: a home screen that shows Home Assistant cards around the dial (lights, other heating zones, speakers, camera snapshots, scenes), an MQTT link to Home Assistant on the local network, a Home Assistant integration for picking and ordering cards, and a signed update system that shows up as a normal update entity. They say they ran it the way they run software at work as a head of product: strict instructions and acceptance criteria for Claude Code, and every change tested on the real thermostat rather than a simulator. Nest's own software still runs the heating and safety cut-outs underneath.

It works on the poster's UK 3rd gen Nest with a Heat Link, and a few testers from the unfr0zen Discord run it too. They pushed a deliberately broken release to their own unit to check the rollback, and it recovered on its own in about 30 seconds. Scrolling was measured on the device at 60 fps with the slowest frame near 30 ms. An early approach that sent fake input to the Nest software nudged the setpoint and was dropped. In the comments one user got a gen 3 running after some fiddling, while a gen 2 failed to patch with a USB boot error.

Only UK 3rd gen units with a Heat Link have been tested with Fledge; 1st and 2nd gen, US wiring, heat pumps and cooling are untested. Flashing rewrites the NAND on the device that runs your heating, so take the full backup the setup app offers and have another way to heat the house. Matter and Zigbee come from unfr0zen unchanged. The code is on GitHub under GPL-3.0.