Bests & Worsts Reviews from Amazon

I have purchased three of these units and I expected them to perform better than they have. One unit keeps advising that there is smoke in room when there is no sign of smoke. The other units will not advise when one of the units is in a warning mode. I contacted Nest about my issue and they advised that they would send out a new unit. Instead, they sent out batteries. When I called back to discuss with them, I was advised that my unit is out of warranty and there was no one to help deal with my issue. I was a loyal customer purchasing a thermostat, two indoor cameras, two outdoor cameras and three smoke detectors...but I feel like that if I spend $100 on a smoke detector, that it should last more than two years.