A motion sensor uses passive infrared, microwave, or a combination of both to detect movement and trigger a connected action — turning on a light, starting a camera recording, or sending an alarm signal. Sensitivity and detection range vary by technology and by mounting height and angle.
On a real property, common placements are stairwells, garage entries, and side yards where continuous lighting or recording is unnecessary. Passive infrared sensors can be fooled by rapid temperature swings, and outdoor units are prone to false triggers from wind-moved vegetation, insects on the lens, or animals.
Poorly aimed or overly sensitive sensors generate nuisance alerts that lead staff to disable or ignore them, which defeats the purpose; conversely, sensitivity set too low can miss a person moving slowly. Sensors also typically have a brief reset delay after triggering, creating a gap where a second intrusion in quick succession may not register.
In a patrol program, a motion-triggered alert from an alarm panel or monitoring center is dispatched to an officer for a physical check, and repeated false triggers at the same sensor should be flagged for maintenance rather than treated as a real event each time.
Related entries
Official sources
- [1]NIST intrusion detection systems overviewNational Institute of Standards and Technology
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