The Thing was a covert listening device designed by Leon Theremin.

Wikipedia goes on to explain:
“Theremin’s device was used by the Soviet Union to spy on the United States. The device was embedded in a carved wooden plaque of the Great Seal of the United States. On August 4, 1945, a delegation from the Young Pioneer organization of the Soviet Union 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 residential study until it was exposed in 1952 during the tenure of Ambassador George F. Kennan.[3] The existence of the bug was accidentally discovered by a British radio operator who overheard American conversations on an open radio channel as the Russians were beaming radio waves at the ambassador’s office. The Department of State found the device in the Great Seal carving after an exhaustive search of the American Embassy, and Peter Wright, a British scientist and former MI5 counterintelligence officer, eventually discovered how it worked.[4][5] Had the device never been discovered, it could easily have worked indefinitely.”