Abstract: An electronic device for use by recreational divers, that uses ultrasonic signals to measure distance, to indicate relative direction, and to maintain contact between at least two diving partners during a diving session. One of the devices is worn and operated by each diving partner, and each device, through an arrangement of ultrasound transmitters and receiver pairs affixed thereto, monitors relative distance between itself and each other device in use by a diving partner. The device has a user interface, including a plurality of push-buttons and liquid crystal display, to set and indicate relative distance, relative direction, low battery fault, and chime or vibration warning mode. The warning mode alerts a diver when a distance limit between companion divers has been exceeded.