This is one reason why I've never gotten anything more complex than a simple Honeywell programmable thermostat. I haven't felt a real need but I also just don't trust "smart" thermostats not to fail off in the winter which can be a really serious event if you're not around (and I normally travel a lot). There are other failure modes for heating of course but I absolutely don't want to introduce another one for no good reason.
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.
Yeah, I've done some locks and status IOT stuff around the house but I don't trust my rather expensive central air/furnace to nest or my own hacking. The 10 year old thermostat works quite well.
This is my bugbear. All my smart systems are 'who cares'. I really want security, heating, and cooking to be smart as I have specific use cases but I don't have the time to Engineer the systems how I want them. Its particularly annoying as I have all the skills!
You can get an old school mechanical thermostat as a backup. I've suffered a total frozen house disaster in a past place - most of the plumbing wrecked - because of a heat failure during the Christmas break (gas valve in that case though; a mechanical thermostat wouldn't have helped). That's what started the obsession with remote temperature monitoring - I was into DS18B20s before they were cool - and from there it was only a little bit more hacking to just take control as well (so I can control it over the internet the way I like it - ssh!)
I have a couple different temperature monitors. Of course, doesn't necessarily do a lot of good unless I can get someone to do something. And that may not be possible if they're not around or if there's not anything they reasonably can do. As in your example.
But I did get an alarm on a trip a couple years ago and texted a neighbor and she was able to tell me the power went out but it was going to be back soon. Of course, backup generator is an option but it's expensive to do right and unsupervised.
Yup - even if I still only had a simple mechanical thermostat I'd still have a second as a backup. The backup thermostat was easy to add - just wired it in parallel directly next to my furnace in the basement; all I had to do was run the second cable from the second thermostat into the furnace control board and double up the connections on the terminals that call for heat. Cheap insurance that took all of 10 minutes to install.
I've had half a mind to start shutting off my water and draining my pipes before leaving on trips in the winter. We've had frozen pipes several times before, but thankfully PEX doesn't seem to burst. Have been working on fixing the insulation issues that lead to the frozen pipes, which I suppose is probably the better solution. But draining the pipes would be a pretty low effort way to get a bit of added insurance.
Don't drain your p-traps - your house will fill with methane/sewer gas. Don't ignore your sewer pipes either; they can burst too. Instead if you really want to winterize, pour RV antifreeze down all your sinks, toilets, tubs, showers, etc.
RV Antifreeze is also great to pour down all your drains if you aren't going to be in your house for an extended period of time even when it's not freezing cold outside - it evaporates a LOT more slowly than water and thus your home will be far less likely to smell like a sewer when you return.
My dad used to have the operation done in the winter at his house in Maine and it wasn't trivial.
Of course, he just turned off the heat entirely as opposed to protecting against temporary heating loss. That said, I never investigated how easily one could just do such protection on one's own. I have improved insulation over the years but you're presumably still in a bad situation if you have a multi-day power outage in freezing temperatures or your furnace quits.
I know to winterize a camper you fill the water lines with antifreeze. I suppose to be really protected you'd need to go that route.
We live in a townhouse with a garage on the main level, so the water comes in on the main level, but basically all of our plumbing is on the upper levels. I've had several times when dealing with different plumbing issues where I turn off the main water valve, then open all the faucets and let the water drain out through our water heater.
I guess the weakness in that approach would be if there was a bend in the pipe somewhere to not let the water drain fully out, it would still freeze. I guess that's probably why people do the antifreeze method when actually winterizing water lines.
This is one reason why I've never gotten anything more complex than a simple Honeywell programmable thermostat. I haven't felt a real need but I also just don't trust "smart" thermostats not to fail off in the winter which can be a really serious event if you're not around (and I normally travel a lot). There are other failure modes for heating of course but I absolutely don't want to introduce another one for no good reason.
(I don't have AC.)