"Auto-Away saves energy by reducing heating and cooling in empty homes. Instead of having to turn the thermostat down every time you leave the house (and back up when you return), the Nest Learning Thermostat turns itself down automatically when it senses that you’re away."
How does this work then?
"Auto-Away saves energy by reducing heating and cooling in empty homes. Instead of having to turn the thermostat down every time you leave the house (and back up when you return), the Nest Learning Thermostat turns itself down automatically when it senses that you’re away."
http://support.nest.com/article/What-is-Auto-Away