Wow, after my experience with Nest thermostat, there's no way I'd risk having a Nest Smoke Detector. I had Nest Thermostat for 3 months. Initially I loved it, but then it kept "think" I was gone when sleeping on the 3rd floor wake to a freezing house. Ok, minor annoyance, disable that feature. Then after a long business trip I came home late to again find a freezing cool house, but this time the Nest had bricked itself. Rest didn't help, support didn't help. So since there is no manual override, I had to uninstall it and reinstall the 20 year old "programmable" thermostat that actually worked. Since I had to uninstall it I told Nest they could have their brick back and refund me.
Now they want me to take that risk with a smoke alarm bricking itself??? Crazy.