Post-WWII

A major shift came after 1945, when wire and tape recorders became available. While they were not usually advertised as such, many users apparently modified them to make surveillance recordings. The first discussions in the courts of whether or not sound recordings could be admitted as evidence began to appear at this time. The making of secret recordings began to be a common element in the plots of novels and movies, but the size of the machines and their general lack of portability probably made their actual use much less common than that.

It was not until the introduction of the transistor recorder in the early 1950s that secret recording became more common. Shortly after "pocket" size tape and wire recorders appeared, certain companies began promoting their use to make secret recorders. The Minifon, a West German product, was the best-known of these. As Cold War paranoia grew, so too did the making of these secret recordings.