Abstract: A non-invasive active infrared device monitors amphibians and other animals in aqueous environments. An infrared emitter circuit and an infrared detector circuit are secured in a horizontal orientation with respect to each other in a u-shaped Plexiglas structure. A combination of variable resistors, a focusing lens, and a funnel allows the detector circuit to detect a pre-selected size of aquatic animal, and by extension a pre-selected species of aquatic animal. When an aquatic animal of a pre-selected size breaks the infrared beam, an event logger is triggered and records the date and time the beam is broken. This device provides a new and enormously useful system for studying the movement patterns and thus key behavioral traits of aquatic amphibians and other aquatic animals.