During the Cold War, the CIA sent cats outfitted with electronic gear to eavesdrop on the enemy. This and other amazing stories in BB pal Tom Vanderbilt's excellent Smithsonian feature "The CIA's Most Highly-Trained Spies Weren't Even Human." Tom's guide through this strange history was Bob Bailey who trained dolphins, chickens, and the aforementioned cats, all for the military.
From the article:
"We found that we could condition the cat to listen to voices," says Bailey. "We have no idea how we did it. But…we found that the cat would more and more listen to people's voices, and listen less to other things." Working with Robin Michelson, a California otolaryngologist and one of the inventors of the human cochlear implant, the team turned the cat into a transmitter—with, says Bailey, a wire running from the cat's inner ear to a battery and instrument cluster implanted in its rib cage. The cat's movements could be directed—left, right, straight ahead—with ultrasonic sound.