Autonomous Recording Units (ARUs), developed by the Bioacoustics Research Program at Cornell University, are used to continuously record elephant vocalizations in forested areas. These units digitally record acoustic data onto laptop hard-drives using a custom pre-amplifier and data acquisition board powered by truck or lantern batteries. Batteries can power units up to 2.5 months without re-charging. Global positioning system antennas and software allow millisecond accuracy time synchronization. Units are hoisted into trees, to protect them from elephant damage, and left to collect long recordings of elephant vocalizations as well as gunshots and sounds of numerous other vocal species. In 2002, 7 units were placed in an array surrounding Dzanga bai in order to determine the exact location and individual elephant producing a call. This allowed only calls made by elephants within the clearing to be related to elephant numbers from hourly counts. Additionally, it has allowed the behavioral context and demography of the calling elephant to be associated with each recorded call.