It starts by building a schedule. For the first week, users change the temperature normally. The Nest notes their preferred at-home temperature, say 72°F, and also determines appropriate "away" temperatures—60º in winter and 80º in summer, for example. To account for conditions outside, the Nest checks the weather over Wi-Fi, and its indoor humidity sensor tells it when to kick in the fan for comfort. If everyone leaves, a motion sensor signals the processor to activate the away setting.