Trail cameras work by utilizing a complex system of infrared cameras to trigger the main imaging camera. Since standard imaging sensors produce a lot of heat and consume more energy than an infrared sensor, manufacturers opt to use a passive infrared camera to trigger the shutter sequence of the main camera.  Additionally, infrared cameras measure heat differences in the environment to detect whether or not an animal has entered the area. This is beneficial because while the main camera is in a standby state, the onboard computer has not calculated which exposure settings are necessary. If we relied on only the imaging camera to handle the triggering sequence, we could very well miss a multitude of shots for the simple fact that the exposure settings would prevent the camera from seeing any movement.