The problem I have with Nest in particular is that the hardware design assumes Internet will always be available. Heat pump systems regularly have an external

The problem I have with Nest in particular is that the hardware design assumes Internet will always be available. Heat pump systems regularly have an external thermometer to ensure that the heat pump is only operated down into the low 40's (F). After that your auxiliary heat turns on. For some reason Nest chose not to include the requisite hardware to run this feature directly, so it gets outdoor conditions from a weather feed. Of course if internet/wifi goes down, then it just has to assume what the outdoor temp is, which is going to be very suboptimal in either direction. When you're out in the boonies, Internet goes down from time to time and the Nest doesn't handle it well at all. I still use it because I do like how it optimizes heating for occupancy (e.g. much lower setpoints when away/sleeping) and I can't bring myself to drop another $x00 on some alternative that will likely just get sucked into IoT hellscape. DIYing it seems much better. I'm actually starting to DIY a control for my wood stove to help optimize for longer burn times...should be interesting.