Explore the Nest API data model.
Nest released an API today to lots of fanfare, to the point the force.com servers hosting the documentation crashed. But the reference is up and it shows the limitations. You only get the same controls you would expect standing in your hallway with your thermostat or smoke detector. There is no historical data, and the smoke is read only. There is no access the the speech processor or display for alternative uses. It is connected, but a game changer?