Passive Infrared Sensor

A passive infrared sensor detects movement by measuring changes in ambient infrared radiation in its field of view — typically body heat from a person moving across the detection zone. PIR sensors are inexpensive, low-power, and require no active emission, which makes them a common choice for ambient-sensing deployments that support older or disabled people living at home. In telecare and smart-home accessibility research, PIR sensors are used to monitor room occupancy, build activity profiles, detect falls by inference from prolonged immobility, and support 'aging in place' without the privacy cost of video cameras. Limitations include inability to distinguish one person from another, poor sensitivity to slow or stationary movement, and limits on depth and directionality that affect coverage design.