A thermostat has tremendous power: It controls heating and cooling, the most expensive, energy-guzzling system in a house. Until the Nest, thermostats wielded that power blindly. The Nest learns a household's schedule and preferences after just one week and programs itself (and if those preferences change, the Nest adapts accordingly). It uses activity, humidity, and temperature sensors to monitor the indoor climate and adjust it for maximum efficiency.
The Nest can also shut down the air conditioner's compressor a few minutes early to make the most of the cool air still available after it cycles off. The homeowner can always adjust the device from home or the road, but will rarely need to-which makes this the first thermostat truly compatible with people's lives.
Power: Rechargeable lithium-ion battery
Compatibility: 95% of 24-volt systems
Price: $249
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