As clever as smart thermostats can be, they usually have only a limited sense of what's going on in your home. They may know that it's cool in the hallway, but not that it's roasting in the living room. Ecobee may have a better, more holistic approach with its third-generation climate controller, the Ecobee 3. Rather than gradually learn what conditions work best over time, it uses remote sensors to determine which rooms are occupied and whether or not they're at the right temperature. The more detectors you add, the more cozy you're likely to be -- you can have up to 32, if you're determined to warm up your mansion.