Or if you have it installed in your master bedroom, with an en-suite bathroom and a steamy shower. Nothing like having all your smoke alarms go off when you're in the shower! We contacted Nest. Their basic response: "Move the Nest Protect further away from the shower." Or, take the stupid thing off the ceiling and switch back to the previous smoke detector, which would detect smoke but was not fooled by water vapor.
Nest had marketed the device as a smoke alarm that you could silence -- because it would have a period where it would warn you that something was wrong before it triggered the alarm, and it would be possible to manually silence it -- but in my direct experience this period never happened. The Protects always went straight from "normal" to "ALARM" without any warning period. Of course the Protect unit in my kitchen never actually detected kitchen smoke, even when I once burned some food quite severely.
I also had a negative experience with the Nest thermostat. I'm still not sure if I had it wired wrong -- I don't believe so, because I had previously installed cheap-o Honeywell thermostats that worked flawlessly -- but one late spring night I turned on the air conditioner to lower the temperature a few degrees, and then went to bed.
I woke up a few hours later, drenched in sweat. Somehow the unit had commanded "EMER HEAT" on my heat pump instead of air conditioning. My bedroom was 91 degrees Fahrenheit! The target temp was 70F, which the unit was never reaching. But it wasn't smart enough to realize "Hey, my actions are just making the temperature INCREASE, I should stop and flag an error." Nest's response: "that's funny, it shouldn't have done that". I took the things off the wall the next day.
I am now very wary of "smart home" technology. I can't imagine the experience that a non-technically inclined user has...