TL;DR version: A little pricy but I like the Nest Thermostat and Nest Protects.
In June, I installed the Nest Learning Thermostat in my house and over the Thanksgiving holiday I installed a few Nest Protects as well. The integration of the Protects with the Thermostats and the application was really good although the install of one of the Nest Protects didn’t go quite like their install made it out to be. I could go on more about all of it but if you’ve read the reviews online, there isn’t more that I can say that hasn’t already been said. They just work and work well.