An apparatus and method for ultrasonically communicating information from a source to a destination and for acknowledging receipt of that information by the destination. The apparatus includes at least one processor, at least one transceiver, and at least one display device, each display device having...http://www.google.es/patents/US5442343?utm_source=gb-gplus-sharePatente US5442343 - Ultrasonic shelf label method and apparatus
