Manufacturers publish a detection distance, but the real-world figure depends on conditions.

The published spec is measured under controlled conditions: a human-sized target (high thermal mass), walking at a moderate pace, at approximately 20°C ambient temperature.

Real-world factors that reduce effective range:

•        High ambient temperature (thermal contrast collapse, as covered in Q3)

•        Small subject size (a fox has much lower thermal mass than a deer)

•        Slow movement speed

•        Wind and rain (thermal noise in the PIR signal)

As a practical guideline, expect reliable detection at 60–70% of the published maximum range in typical field conditions. For a camera rated at 25 meters, plan camera placement for animals at 15–18 meters.