In 1945 Theremin invented the first covert listening device (or "bug") for spying. Theremin's device was embedded in a carved wooden plaque of the Great Seal of the United States. On August 4, 1945, Soviet school children presented the bugged carving to U.S. Ambassador Averell Harriman, as a "gesture of friendship" to the USSR's World War II ally. It hung in the ambassador’s Moscow office until 1952, when the bug was discovered by a British radio operator who heard conversations on an open radio channel. The CIA found the device in the Great Seal carving. Peter Wright, a scientist and former MI5 counterintelligence officer, eventually figured out how it worked.