The Nest features an auto-away function that can detect when you've left your home and automatically switch to an "away temperature" to avoid heating or cooling an empty house.

This small board houses the two motion sensors (long and short range) responsible for this feature. These sensors are capable of detecting movement within a 150° field of vision.

Through a rather clever design, the sensor board has no cable connecting it to the motherboard. Instead, it rests on four screw posts that make up its contacts.