Which principle do PIRs utilize for motion detection?

PIRs, or Passive Infrared Sensors, operate based on the principle of detecting infrared radiation emitted by objects, particularly warm bodies like humans and animals. These sensors are designed to sense changes in the levels of infrared radiation in their environment. When a warm object moves within the sensor's field of view, the PIR detects the difference in infrared signals, triggering the alarm system.

The technology relies on the fact that all objects with a temperature above absolute zero emit infrared radiation. The sensor uses this radiation to determine if there is motion. The sensitivity of PIRs to changes in infrared energy is what makes them effective in security systems. By only responding to changes in infrared levels, PIRs can effectively distinguish between normal ambient conditions and the presence of a moving warm body.

This principle makes PIRs particularly useful in burglar alarm systems, as they can efficiently detect unauthorized movement while minimizing false alarms that might be triggered by other forms of motion or environmental changes.