Studies of small mammal biology often employ the method of capturing animals by a line of traps deployed with 3-5 meter spacing for a given time interval. This is a universal method applicable for a wide range of tasks, including investigation of the composition and numbers of parasites in small mammals. One of the shortfalls of this method, however, is that the time of capture is not known. Ectoparasites tend to escape from the dead host, and having no information on how long the animal remained trapped makes it difficult to accurately interpret the results regarding infection rates, and species with epidemiological implications are no exception. To handle this issue, we created a trap line with automatic recording of the time of capture. The device was designed for the widely used, all-purpose, and inexpensive snap traps (bar-type). Capture time in all traps in the line is recorded and memorized using a standard microcontroller. When the snap trap is initially set, the circuit is closed. This closed circuit status of each trap is monitored by microcontroller program. When the trap snaps the animal, the circuit is interrupted, and this event is registered by the microcontroller, and the trap number and capture time are recorded on a microSD memory card. The code was written in C++ language in Atmel Studio environment. The results permit describing the circadian activity of small mammals, as well as quantifying the actual losses (undercounting) of ectoparasites depending on how long the dead animal remained in the trap.