Eavesdropping device in a wooden panel

Back in 1945, Soviet schoolchildren gifted an American ambassador a precious wood piece with an image of the U.S. coat of arms on it.

The "bug" device was so hidden that the American secret services did not notice anything, while the Soviet ones listened to the ambassador's conversations for another 8 years. After the discovery, the device was presented to the UN as evidence of Soviet intelligence activities.