I believe that's a recent requirement in California for new or updated dwellings. See R314.5: http://osfm.fire.ca.gov/firelifesafety/pdf/Smoke%20Alarm%20Task%20

I believe that's a recent requirement in California for new or updated dwellings. See R314.5: http://osfm.fire.ca.gov/firelifesafety/pdf/Smoke%20Alarm%20Task%20Force/R-32%202010%20CA%20Residential%20Code.pdf http://osfm.fire.ca.gov/firelifesafety/pdf/Smoke%20Alarm%20T... Also interesting is that quite a few municipalities forbid connecting the fire alarm system to any external system, unless the external system is UL listed. Could be some regulatory hurdles in Nest's future.