Vulpo 1.3Updated
Home Assistant on Apple Watch
The official Home Assistant app includes a watch app that runs actions, scripts and scenes, talks to Assist and shows complications on watchOS 9 and newer. For direct device controls on the wrist, Vulpo and Wrist Assistant add full watch apps; Vulpo's also works over Wi-Fi or LTE without the iPhone.
The official watch app
The official app's watch companion is set up from the iPhone app. According to its documentation it runs actions, scripts and scenes, lets you talk to Assist, and offers complications for the watch face in graphic circular, rectangular, corner and modular sizes, filled from templates. It needs watchOS 9 or newer on an Apple Watch Series 4 or newer.
Controlling devices directly
If you want to dim a light, set a thermostat or start a vacuum from the watch rather than run a script for it, use a watch app with device controls.
Vulpo
Glances, favorites, scenes and pinned cards in pages you arrange on the iPhone; Digital Crown controls for lights, covers, climate, fans, locks, media, vacuums and alarm panels; sensor history and complications for any entity. The watch app is free, needs watchOS 26 and works on its own over Wi-Fi or LTE. Vulpo is made by the publisher of this site.
Wrist Assistant
Custom watch pages designed on the iPhone, with live cameras, scenes, scripts and automations, according to its App Store listing.
Without the iPhone
A watch app can reach Home Assistant on its own when the watch is on Wi-Fi or has LTE, as long as your Home Assistant server is reachable from where the watch is. Away from home that means an external URL, for example through Nabu Casa or your own domain. Vulpo's watch app connects directly in both cases.
Questions
Can I put a Home Assistant sensor on my watch face?
Yes. The official app offers template-based complications, and Vulpo offers complications for any entity. Complications refresh on the schedule watchOS allows; Vulpo's refresh about every 15 minutes.
Which Apple Watch do I need?
The official watch app needs watchOS 9 on a Series 4 or newer. Vulpo's watch app needs watchOS 26.
Sources
Facts about other apps come from their App Store listings and documentation as of the date above. Home Assistant is a trademark of the Open Home Foundation; Vulpo is not affiliated with it. Corrections: josh@vulpo.app.