The Orbit detects motion by means of a PIR sensor, a passive infrared sensor. This sensor detects emitted infrared energy from objects (humans and animals, but also cars) in the form of heat.
In general differences of around 5-10º Celsius compared with the ambient temperature in the field of view and within a 2-5m /6.5-16.4ft (depending on the angle) range of the camera are detected.