I'm an iOS developer and my app (AirCompare) controls a HomeKit-enabled thermostat based on the weather and other factors. A user has an Ecobee 4 and it occasionally behaves in unexpected ways. The Ecobee documentation...well, basically there isn't any.
Here's one example I discovered last year: The thermostat may be set to "Off", not heating or cooling, but changing the temperature set point will trigger the thermostat to change the mode to achieve that new set point. That's understandable but my Ecobee 3 does not change mode on its own, so it was a surprise.
Now somehow an Ecobee 4 under control of my app self-changed its mode to "Auto", and proceeded to turn on my user's furnace despite having the windows open to cool off the house. I'm not quite sure what triggered that.
Does anyone know where to find any references on this? This is the first thread on SO to include both "Ecobee" and "HomeKit", so I'm not super optimistic. Please surprise me!
I used esp32 here is the code file. I am have not worked with Ecobee but I am sure it will help you. Checkout here for further docs.