My guess is that if it was recessed in the ceiling it might not work properly since the smoke could roll below it.
For those saying that the wave to turn off was a dumb idea. Think about why they did it. I wonder how many smoke alarms are diabled because of false alarms. They may have disabled them because it was to much of a hassle/hard to turn off.
The wave to turn off was/is a great idea. With traditional alarms you have to pull it down and remove the battery to shut it up. The wave override doesn't work if there is "too much smoke" Not sure how that is defined.
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I bought one because I was generally happy with my Nest thermostat however between the disabling of the wave feature, their decision to artificially limit the motion detector in the battery version and the dullness of the night light, it's been a compete waste of money.
They should offer refunds. What's the selling point now? You can check the battery status via an app? Big deal.
As another person with this and a Nest thermostat. Once of the nicer safety features is if CO is detected it turns the furnace off, the probably source of CO in most instances. The second feature is all the alarms go off if an issue is detected and they announce what device detected the alarm situation. Doing this without having to wire all the alarms together.