Re: Nest's smartphone app really is the best
You'd be surprised - the alarm I ripped out when it broke is still a current model, was 3 years old when I disposed of it.
Not an IC on it.. all transistor based, so it was about 5 times the size it should be about 12" by 8".. I doubt the design has changed since the 1980s.
Replaced with an ESP8266 that does the same job in a 1.5 inch square piece of silicon (and gives me wireless status as well plus remote arming if I'm in wifi range).