Trailcameras only take pictures if there is actual activity in front of the camera. For this they depend on a so-called passive infrared (PIR) sensor. This advanced sensor activates the camera when it detects a moving heat source. Camera traps therefore do not react to movement alone (i.e. a moving branch or a falling leaf), but only if the moving object is warmer or colder than its immediate surroundings. This means that the PIR sensor actually determines the quality of a trailcamera and is perhaps the most important part of a camera trap. Click here to learn more about how the PIR sensor works.