The Nest thermostat is priced at $249.95 in the U.S. online store and is just one of a number of products featured in Apple's App-Enabled Accessories section. The thermostat can be controlled via a free universal iOS app [App Store], with access to controls also available through web browsers.
The Nest Learning Thermostat helps you stop wasting energy, while providing control using your iPhone, iPad, iPod touch, or Mac. Consider that your thermostat controls about half your energy bill—more than TV, appliances, and lighting combined. But it's wasting energy every time it turns on the heating or cooling system in an empty house. The Nest Learning Thermostat solves this problem by programming itself, turning itself down when you're away, and keeping track of your energy use.