It is uncertain who invented the first electric hearing aid, it may have been the Akoulathon, invented in 1898 by Miller Reese Hutchinson and made and sold (1901) by the Akouphone Company of Alabama for $400.
A device called the carbon transmitter was needed in both the early telephone and the early electric hearing aid. This transmitter was first commercially available in 1898 and was used to electrically amplify sound. In the 1920's, the carbon transmitter was replaced by the vacuum tube, and later by a transistor. Transistors allowed electric hearing aids to become small and efficient.