The Minfon brochures advertise the equipment as "smallest pocket dictating machine" and "speaking agenda", sold at the time with the microphone, the headphone and one bobbin for the amount of Fr. 950. The Hanhart chronograph watch with a microphone instead of a movement was then added in order to use the device for spying purposes.
The Minifon, an ultra-miniaturized, battery operated magnetic recording device, was developed by Protona GmbH in Hamburg in the 1950s. The company's initial idea was the production of a pocket dictating machine which people like salesmen could take with them when travelling. But once on the market, the Minifon's producers discovered that many people took advantage of the recorder's small size to make secret recordings which were used, for example, as evidence in court.
In the years to follow and with the increasing Cold War paranoia, the machines were upgraded to multi-purpose devices with a variety of optional equipment. One of the most interesting options was certainly the miniature microphone for "spy" recordings disguised as a wristwatch.
For an illustration and short description of another "Minifon" tape recorder with watch see Military Timepieces by Konrad Knirim, p. 593.