The Thing, also known as the Great Seal bug, was one of the first covert listening devices (or "bugs") to use passive techniques to transmit an audio signal. It was concealed inside a gift given by the Soviet Union to W. Averell Harriman, the United States Ambassador to the Soviet Union, on August 4, 1945. Because it was passive, needing electromagnetic energy from an outside source to become energized and active, it is considered a predecessor of radio-frequency identification (RFID) technology. Creation The Thing was designed by Soviet Russian inventor Leon Theremin,<ref>Glinsky, Albert, Theremin: Ether Music and Espionage, University of Illinois Press, Urbana, 2000</ref> best known for his invention of the theremin, an electronic musical instrument. In Russian, the device is called Эндовибра́тор (endovibrator). Installation and use The device, embedded in a carved wooden plaque of the Great Seal of the United States, was used by the Soviet government to spy on the US. On August 4, 1945, several weeks before the end of World War II, a delegation from the Young Pioneer Organization of the Soviet Union presented the bugged carving to Ambassador Harriman, as a "gesture of friendship" to the Soviet Union's war ally. It hung in the ambassador's Moscow residential study for seven years, until it was exposed in 1952 during the tenure of Ambassador George F. Kennan. Operating principles The Thing consisted of a tiny capacitive membrane connected to a small quarter-wavelength antenna; it had no power supply or active electronic components. The device, a passive cavity resonator, became active only when a radio signal of the correct frequency was sent to the device from an external transmitter. This is referred to in NSA parlance as "illuminating" a passive device. Sound waves (from voices inside the ambassador's office) passed through the thin wood case, striking the membrane and causing it to vibrate. The movement of the membrane varied the capacitance "seen" by the antenna, which in turn modulated the radio waves that struck and were re-transmitted by the Thing. A receiver demodulated the signal so that sound picked up by the microphone could be heard, just as an ordinary radio receiver demodulates radio signals and outputs sound. Theremin's design made the listening device very difficult to detect, because it was very small, had no power supply or active electronic components, and did not radiate any signal unless it was actively being irradiated remotely. These same design