Game cameras (Passive Infrared: PIR) are valuable sampling tools commonly used to monitor use of undercrossings by wildlife but are challenged to reliably sample small animals, particularly those that are endothermic. We introduce a novel active camera trigger system (HALT) that enables the reliable and efficient use of wildlife cameras for sampling a vast array of small animals. It far surpasses the detection ability of PIR cameras in monitoring for reptiles, amphibians, and large invertebrates and eliminates problems such as high rates of false triggers and high variability in detection rates among cameras and study locations. The HALT trigger system couples to a digital PIR camera and is designed to detect small animals traversing constricted pathways such as small culverts and wildlife tunnels. Larger underpasses and culverts can also be effectively monitored for small animals by using the HALT in combination with drift fencing. Batteries only need to be replaced every 3-4 months depending upon the level of animal activity. We present an example of using the HALT system to monitor California tiger salamander use of road undercrossings in Stanford, California.