Motion detectors are commonly found in alarm systems and automated lighting systems. There are several senor technologies, but the most common is Passive Infra Red, or PIR. PIR detectors has a sensitive infra-red sensor behind a Fresnel-lens that splits the detection area into vertical or horizontal sections. When a warm body moves between the fields, the sensor will detect rapid changes, and trigger a relay.
More advanced sensors combine multiple detection methods to reduce the risk for false alarms while keeping a high sensitivity to motion.
The output on most motion sensors is a simple relay contact. The contact closure can trigger the ezeio logic to send an alarm, turn on a light or start a fan. For a more creative solution involving motion detection, read about out Smart Internet connected Door Chime here.