The CIA tried to use cats as spies.

In the 1960s, the CIA spent 5 years working on the technology to implant listening devices into a cat and train her to covertly listen in on conversations. The cat was rigged with a microphone in her ear and an antenna running down her back. Because of the cat’s small size the transmitter was not equipped with a bigger long-lasting battery. This meant that the cat could only record conversations for a short time. In addition to that minor inconvenience, the cat also performed very poorly in its first field test. The spy-cat was hit by a car en route to a Soviet meeting place.
(source)