Edison Records
Thomas A. Edison invented the phonograph, the first device for recording and playing back sound, in 1877. After patenting the invention and benefiting from the publicity and acclaim it received, Edison and his laboratory turned their attention to the commercial development of electric lighting, playing no further role in the development of the phonograph for nearly a decade. Edison's original phonograph recorded on sheets of tinfoil and was little more than a crude curiosity, although one that fascinated much of the public. These earliest phonographs were sold mainly to entrepreneurs who made a living out of traveling around the country giving "educational" lectures in hired halls or otherwise demonstrating the device to audiences for a fee. The tinfoil phonograph was not fit for any real practical use and public interest soon waned.
Miller Reese Hutchison
In 1905 Hutchison turned over the rights for the Acousticon to Kelley Monroe Turner (1859–1927). Turner would improve hearing aids (such as adding a volume control) and apply the technology to other products. One was the dictograph, which was an early hands-free inter-office intercom system. Turner's General Acoustic Company was renamed Dictograph Products Company because of the market success of the dictograph.
One of the first electric eavesdropping devices was called the Detective Dictograph, announced in 1910. 
The carbon technology for hearing aids was used until the miniature vacuum tube replaced it in the 1940s. Advertisements in 1947 still carried the Acousticon brand name, and invoked Queen Alexandra's coronation image of 45 years earlier; model names were "Coronation" and "Imperial".