It's been less than a year since former iPod chief Tony Fadell and his team announced the high-end Nest thermostat, but they're already improving things: the new second-generation Nest is 20 percent slimmer and adds compatibility with 95 percent of low-voltage home HVAC systems, up from 75 percent. "We thought we could make it even better," says Maxime Veron, Nest's head of product marketing.

The slimdown is courtesy of a refined design that features a brushed stainless steel ring that serves as both control dial and outer housing — the older Nest placed the dial up and away from the main housing. Inside, a new "invisible" front plate hides the sensors without the open grille of the previous version, and a revised backplate with a pair of new connector allows the new Nest to control virtually every major kind of heating and cooling system on the market. That includes second-stage air conditioning systems, third-stage heating and emergency heat for heat pumps, and humidifiers and dehumidifiers.

Nest is also rolling out version 3.0 of its software, which will also work with the previous Nest units — the company doesn't expect people to upgrade their thermostats every year. The 3.0 software's biggest upgrade is System Match, which fine tunes the software for specific types of heating and cooling systems: forced-air heating and cooling systems start up earlier, while radiant heating and heat pump systems receive similar adjustments. The auto-away feature is also more aggressive and can kick in as soon as 30 minutes after you leave the house, while the auto scheduler can program itself in the dual heating and cooling mode.

Auto-away has been improved "big time," says Veron. "We've found people are extremely predictable, especially in the morning." The system won't kick in unless it's absolutely sure you're out of the house — it won't kick in if you're working from home, for example.

"We're going to make a lot of people very happy"

Nest's smartphone and web apps have also been updated to version 3.0 to support the new features, and they'll have more granular information on energy usage. Nest has also improved the Android app to better support 7-inch tablets like the Kindle Fire and the Nexus 7. "We're going to make a lot of people very happy," says Veron. "When Amazon released the Kindle Fire, it really changed the landscape, and then the Nexus 7 came out... these are the two we see taking off."

Nest's 3.0 software update will hit current devices tonight, while the new Nest is available for pre-order now from Nest's web site for $249 and will ship in a couple weeks. It'll show up at Lowe's, Amazon, and Apple's online store at the end of the month — until then, the current Nest will fall to $229 at Lowe's while supplies last.