Popular in the 1970's the acoustic coupler was a device that allowed a computer to connect to other computers using a telephone handset. The first acoustic couplers used a telephone handset and transmitted at speeds of up to 300 baud. To transmit information the acoustic coupler converts data into sound signals, sends those signals over the phone line, and then the receiving acoustic coupler interpreted those signals. The picture is an example of an acoustic coupler available through Konexx.
Today, data transmission over phone lines happens via modem instead of the acoustic coupler because of the dependability, speed, and ease of use. Although acoustic couplers are rarely used today, they may still be a solution for travelers who do not have access to a modem or network connection.