Shoe with Heel Transmitter
c. 1960s, USSR, KGB issue

The shoe transmitter's microphone and batteries were imbedded in the heel of a target's shoe. Someone close to the target (usually a maid or valet with access to the individual's clothing) would lay out the rigged shoes for the target and pull out a white pin from the heel to activate the transmitter. The target would then transmit all conversations to a nearby monitoring post.