Research overview: passive infrared sensor technology in camera traps

Most modern camera traps fire when a passive infrared sensor detects a moving heat signature, the contrast between a warm animal and its cooler background. This overview explains how PIR sensors work, why their effective range and reliability vary with ambient temperature, animal size and surface temperature, distance, angle of approach, and vegetation, and how these dependencies create detection biases that favor large, warm-bodied animals crossing perpendicular to the sensor. It covers trigger speed, recovery time, and the detection-zone shape that together determine which animals are captured and which slip through. Because PIR behavior shapes the data feeding every density and occupancy method, understanding it is essential for interpreting results and for photographers seeking dependable captures of felids in varied climates, from tropical forest to snowy mountains.