1960s USA Moscow embassy...
Soviet "gift" of seal OF USA, contained passive UHF cavity microphone eavesdropping device.
When illuminated by a beam of radio transmission at the cavity frequency, a réfection was emitted with sound modulated.
This the KGB, GRU, GPU, Spied on USA for many years before the mendacidty of the Russkis was exposed.
Similaires to the laser beam off the window spy microphone.
Jon