I was going through some old tapes about the mob that were on A & E a few years ago and was astonished to see that the Feds were using hidden cameras as far back as 1939 in an attempt to catch mobsters.

In Marshalko's book The World Conquerers, it is disclosed that in the Budapest uprising of 1956(before Russian tanks came), many tapes were discovered proving that almost everyones phone was tapped and their conversations were being recorded.

The present technology is most likely far superior to that.