Trail cameras use Passive Infrared (PIR) sensors to detect motion. PIR sensors measure changes in infrared radiation (heat) across their detection zone. The key factors affecting detection range are:

• Temperature differential -- The greater the difference between the animal's body temperature and the ambient air, the easier it is for the PIR sensor to detect motion
• Animal size -- Larger animals emit more infrared radiation and are detectable at greater distances
• Cross-sensor movement -- Animals moving across the sensor's field detect much better than those walking directly toward the camera
• Vegetation -- Thick brush blocks infrared radiation and reduces effective range

Manufacturers test detection range under ideal conditions. Real-world performance is typically 60-80% of the rated specification.