All told, Nest says the second-gen thermostat is 20 percent thinner than the original. Take a look at our hands-on photos and you'll notice some more subtle changes: the band is now made entirely of stainless steel, with no plastic bits. And whereas there used to be a grille on the front face, the sensors are now hidden under transparent plastic, making for an even less cluttered design. The back plate, meanwhile, has been updated so that it now supports second-stage cooling systems, three-stage heating, humidifiers, dehumidifiers and emergency heat through heat pumps. According to Nest, that extra support should make the thermostat compatible with 95 percent of heating and cooling systems, up from 75 percent on last year's model. Keep in mind, though, that that figure only applies to low-voltage systems in the US. (The Nest is only available in the United States and Canada.)
On the software side, the most impressive new feature might be System Match, which learns not just your schedule, but the idiosyncrasies of your home. For example, if you live in an old Victorian with a decades-old heating system, Nest will learn that it takes your house longer to warm up than, say, a new construction. So, once it knows how long it takes your heating system to reach a given set point, it can turn up the heat further in advance so that you don't wake up to a chilly house.
Other new features include Auto-Away, which uses your scheduling patterns to predict when there won't be anybody at home. So, instead of just relying on proximity sensors to determine that everyone has left the house, it can automatically lower the temperature at certain times of day when people usually aren't around. Additionally, the auto scheduling feature has been improved such that the Nest can now learn when it's set to Heat / Cool mode. Finally, the mobile apps have been updated so that you can see who changed the set point, and when. (As if you didn't already know you and your spouse were engaged in a passive-aggressive tug-of-war over the temperature.) All those updates should be live in their respective app stores by tonight, so check back if you don't see them just yet.