Does Ecobee require an app and account to be activated, or is it something that HomeKit just detects on the LAN?

I know they used to be Home Assistant capable but required an API key which they will no longer give out. Seems like no fully local control to me. I believe my app stops working when the Internet goes out but it's been a bit.

My ecobee has been working a for year with no internet.

Of course the app stops working, but that’s expected from a WiFi product.

Oh really? Weird. I did need to do some developer API key thing to get mine in HA, and it's awesome. All sensors and controls work great[1].

Since it's Homekit compatible though, you can go that route. HA easily discovers anything HK compatible as soon as you connect it to your network. So you connect Ecobee to HA with the HomeKit protocol in lieu of connecting it with Apple's stuff.

[1] ...and anything's better than the asinine on-device UI that Ecobee "updated" to a couple years ago (ask yourself: what would a foolish inexperienced "uX dEsIgNeR" do to ruin a plain old thermostat UI? It's that.)

I've had both and am much happier with Ecobee.

same here. had 2 nests and 2 ecobees. the only ecobee quirk i find after 9 years of ecobees is that the weather calculation is way off if you live near microclimates. i'm not sure if they use your postal zipcode, or use a map from IP address to more accurate weather, but it's normally showing weather from 10 miles away.

My wife can ask google home for the weather forecast and it is correct. I ( the account holder ) can ask it when right beside her and it will provide weather prediction for a location 30km away.

for extra fun. weird bugs in both it seems

I was really disappointed with the lack of analytics / historical data.

Thankfully the open source beetstat makes ecobee a lot more useful, with full history and graphs for heat/cool runtime, aux heat, indoor/outdoor humdity, etc