here's their white-paper PDF: http://assets-www.nest.com/white_papers/efficiency-simulation-white-paper.pdf http://assets-www.nest.com/white_papers/efficiency-s

here's their white-paper PDF: http://assets-www.nest.com/white_papers/efficiency-simulation-white-paper.pdf http://assets-www.nest.com/white_papers/efficiency-simulatio... "The auto-away feature is based on algorithms that interpret occupancy sensor data and provide a confidence determination of whether or not the occupants are away from the home. When the confidence level is high that occupants are away, the autoEaway feature makes a decision to override the existing schedule to save additional energy" it has sensors for movement, temperature, humidity, and light.