Abstract: An ultrasonic pool occupant sensing device capable of using ultrasonic pulses to analyze the occupancy level of a swimming pool. An ultrasonic transducer sends and receives ultrasonic pulses. A front end electronics has a driver for controlling the transducer, a pre-amplifier, band-pass filter, and amplifier combination for filtering received signals. The digital processing unit contains a timer unit for generating pulses, an AD converter for digitizing received pulses, a signal processor for determining data about the return pulse, and an I/O unit for transmitting data to the central processing unit. The data may be an estimate of the number of people in the sensor range, or it may be data about the return pulse that can be analyzed by the central processing unit.