Knowing the detection zone pattern can help produce more “true triggers” and fewer “false triggers.” In an earlier post Deep Tech: Trail Camera PIR Sensors I covered some of the details of PIR sensors. Based on feedback from subscribers, though, I realized that I had missed some subtle aspects of the Fresnel lens optics and detection zones for PIR sensors. In this post, I look more closely at trail camera detection zones, and how they work. I also give a straightforward way to find the detection zones in most cameras. I use this method to measure the detection zones for three camera models.