A bar code scanner includes aseparate transmitter and receiver, each being able to ultrasonically transmit and receive data, respectively. The receiver transmits an acknowledgement signal when a protocol is received, and sends the acknowledgement signal to the transmitter which, unless it receives the...http://www.google.se/patents/US5959284?utm_source=gb-gplus-sharePatent US5959284 - Bar code reading and data collection unit with ultrasonic wireless data transmission
