The Thing (listening device)

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Replica of the Great Seal which contained a Soviet bugging device, on display at the NSA's National Cryptologic Museum. Bugged-great-seal-closed.jpg
Replica of the Great Seal which contained a Soviet bugging device, on display at the NSA's National Cryptologic Museum.
The seal opened exposing the Soviet bugging device, on display at the NSA's National Cryptologic Museum. Bugged-great-seal-open.jpg
The seal opened exposing the Soviet bugging device, on display at the NSA's National Cryptologic Museum.

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 activate, it is considered a predecessor of Radio-Frequency Identification (RFID) technology. [1]

A covert listening device, more commonly known as a bug or a wire, is usually a combination of a miniature radio transmitter with a microphone. The use of bugs, called bugging, is a common technique in surveillance, espionage and police investigations.

Soviet Union 1922–1991 country in Europe and Asia

The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was a socialist state in Eurasia that existed from 30 December 1922 to 26 December 1991. Nominally a union of multiple national Soviet republics, its government and economy were highly centralized. The country was a one-party state, governed by the Communist Party with Moscow as its capital in its largest republic, the Russian Soviet Federative Socialist Republic. Other major urban centres were Leningrad, Kiev, Minsk, Alma-Ata, and Novosibirsk.

W. Averell Harriman American businessman, politician and diplomat

William Averell Harriman, better known as Averell Harriman, was an American Democratic politician, businessman, and diplomat. The son of railroad baron E. H. Harriman, he served as Secretary of Commerce under President Harry S. Truman and later as the 48th Governor of New York. He was a candidate for the Democratic presidential nomination in 1952 and 1956, as well as a core member of the group of foreign policy elders known as "The Wise Men".



The Thing was designed by Soviet Russian inventor Léon Theremin, [2] best-known for his invention of the theremin, an electronic musical instrument.

Léon Theremin Russian inventor

Lev Sergeyevich Termen, or Léon Theremin in the United States, was a Russian and Soviet inventor, most famous for his invention of the theremin, one of the first electronic musical instruments and the first to be mass-produced. He also devised the interlace technique for improving the quality of a video signal, still widely used in video and television technology. His listening device, "The Thing", hung for seven years in plain view in the United States Ambassador's Moscow office and enabled Soviet agents to eavesdrop on secret conversations.

Theremin electronic music instrument

The theremin is an electronic musical instrument controlled without physical contact by the thereminist (performer). It is named after the Westernized name of its Soviet inventor, Léon Theremin, who patented the device in 1928.

Installation and use

The device, embedded in a carved wooden plaque of the Great Seal of the United States, was used by the Soviets 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 USSR'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. [3]

Great Seal of the United States national seal

The Great Seal of the United States is used to authenticate certain documents issued by the federal government of the United States. The phrase is used both for the physical seal itself, which is kept by the United States Secretary of State, and more generally for the design impressed upon it. The Great Seal was first used publicly in 1782.

World War II 1939–1945 global war

World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war.

Allies of World War II Grouping of the victorious countries of World War II

The Allies of World War II, called the United Nations from the 1 January 1942 declaration, were the countries that together opposed the Axis powers during the Second World War (1939–1945). The Allies promoted the alliance as a means to control German, Japanese and Italian aggression.

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 currently referred 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.

Antenna (radio) electrical device which converts electric power into radio waves, and vice versa

In radio engineering, an antenna is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves. In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment.

Microwave cavity

A microwave cavity or radio frequency (RF) cavity is a special type of resonator, consisting of a closed metal structure that confines electromagnetic fields in the microwave region of the spectrum. The structure is either hollow or filled with dielectric material. The microwaves bounce back and forth between the walls of the cavity. At the cavity's resonant frequencies they reinforce to form standing waves in the cavity. Therefore, the cavity functions similarly to an organ pipe or sound box in a musical instrument, oscillating preferentially at a series of frequencies, its resonant frequencies. Thus it can act as a bandpass filter, allowing microwaves of a particular frequency to pass while blocking microwaves at nearby frequencies.

Radio technology of using radio waves to carry information

Radio is the technology of using radio waves to carry information, such as sound and images, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as their amplitude, frequency, phase, or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form.

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 features, along with the overall simplicity of the device, made it very reliable and gave it a potentially unlimited operational life.

Technical details

The device consisted of a 9-inch (23 cm) long monopole antenna (quarter-wave for 330 megahertz (MHz) frequencies, but able to also act as half-wave [at 660 MHz] or full-wave [at 1320 MHz], the accounts differ - given the radio technology of the time, the frequency of 330 MHz is most likely) — a straight rod, led through an insulating bushing into a cavity, where it was terminated with a round disc that formed one plate of a capacitor. The cavity was a high-Q round silver-plated copper "can", with the internal diameter of 0.775 in (19.7 mm) and about 11/16 in (17.5 mm) long, with inductance of about 10 nanohenry. [4] Its front side was closed with a very thin (3 mil, or 75 micrometers) and fragile conductive membrane. In the middle of the cavity was a mushroom-shaped flat-faced tuning post, with its top adjustable to make it possible to set the membrane-post distance; the membrane and the post formed a variable capacitor acting as a condenser microphone and providing amplitude modulation (AM), with parasitic frequency modulation (FM) for the re-radiated signal. The post had machined grooves and radial lines into its face, probably to provide channels for air flow to reduce pneumatic damping of the membrane. The antenna was capacitively coupled to the post via its disc-shaped end. The total weight of the unit, including the antenna, was 1.1 ounces (31 grams).

Monopole antenna

A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.

Hertz SI unit for frequency

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), terahertz (1012 Hz, THz), petahertz (1015 Hz, PHz), and exahertz (1018 Hz, EHz).

Inductance electrical property

In electromagnetism and electronics, inductance is the geometric property of a collection of electrical conductors that allows do describe the effects of electromagnetic induction by which a change in electric current through the conductors induces an electromotive force (voltage) in itself and in the other conductors. The property describing the effect of one conductor on itself is more precisely called self-inductance, and the properties describing the effects of one conductor with changing current on nearby conductors are called mutual inductances. The notion of inductance is especially handy for dealing with discrete, concentrated components at low frequencies.

The length of the antenna and the dimensions of the cavity were engineered in order to make the re-broadcast signal a higher harmonic of the illuminating frequency. [5]


A harmonic is any member of the harmonic series. The term is employed in various disciplines, including music, physics, acoustics, electronic power transmission, radio technology, and other fields. It is typically applied to repeating signals, such as sinusoidal waves. A harmonic of such a wave is a wave with a frequency that is a positive integer multiple of the frequency of the original wave, known as the fundamental frequency. The original wave is also called the 1st harmonic, the following harmonics are known as higher harmonics. As all harmonics are periodic at the fundamental frequency, the sum of harmonics is also periodic at that frequency. For example, if the fundamental frequency is 50 Hz, a common AC power supply frequency, the frequencies of the first three higher harmonics are 100 Hz, 150 Hz, 200 Hz and any addition of waves with these frequencies is periodic at 50 Hz.

An nth characteristic mode, for n > 1, will have nodes that are not vibrating. For example, the 3rd characteristic mode will have nodes at L and L, where L is the length of the string. In fact, each nth characteristic mode, for n not a multiple of 3, will not have nodes at these points. These other characteristic modes will be vibrating at the positions L and L. If the player gently touches one of these positions, then these other characteristic modes will be suppressed. The tonal harmonics from these other characteristic modes will then also be suppressed. Consequently, the tonal harmonics from the nth characteristic modes, where n is a multiple of 3, will be made relatively more prominent.

The original device was located with the can under the beak of the eagle on the Great Seal presented to W. Averell Harriman (see below); accounts differ on whether holes were drilled into the beak to allow sound waves to reach the membrane. Other sources say the wood behind the beak was undrilled but thin enough to pass the sound, or that the hollowed space acted like a soundboard to concentrate the sound from the room onto the microphone.

The illuminating frequency used by the Soviets is said to be 330 MHz. [6]


The existence of the bug was discovered accidentally by a British radio operator at the British embassy who overheard American conversations on an open radio channel as the Soviets were beaming radio waves at the ambassador's office. An American State Department employee was then able to reproduce the results using an untuned wideband receiver with a simple diode detector/demodulator, [7] similar to some field strength meters.

Two additional State Department employees, John W. Ford and Joseph Bezjian, were sent to Moscow in March 1951 to investigate this and other suspected bugs in the British and Canadian embassy buildings. They conducted a technical surveillance counter-measures "sweep" of the Ambassador's office, using a signal generator and a receiver in a setup that generates audio feedback ("howl") if the sound from the room is transmitted on a given frequency. During this sweep, Bezjian found the device in the Great Seal carving. [7] :2

The Federal Bureau of Investigation set about to analyze the device, and hired people from the British Marconi Company to help with the analysis. Marconi technician Peter Wright, a British scientist and later MI5 counterintelligence officer, ran the investigation. [7] He was able to get The Thing working reliably with an illuminating frequency of 800 MHz. The generator which had discovered the device was tuned to 1800 MHz.

The membrane of the Thing was extremely thin, and was damaged during handling by the Americans; Wright had to replace it.

The simplicity of the device caused some initial confusion during its analysis; the antenna and resonator had several resonant frequencies in addition to its main one, and the modulation was partially both amplitude modulated and frequency modulated. The team also lost some time on an assumption that the distance between the membrane and the tuning post needed to be increased to increase resonance.


Wright's examination led to development of a similar British system codenamed SATYR, used throughout the 1950s by the British, Americans, Canadians and Australians.

There were later models of the device, some with more complex internal structure (the center post under the membrane attached to a helix, probably to increase Q). Maximizing the Q-factor was one of the engineering priorities, as this allowed higher selectivity to the illuminating signal frequency, and therefore higher operating distance and also higher acoustic sensitivity. [7]

The CIA ran a secret research program at the Dutch Radar Laboratory (NRP) in Noordwijk (Netherlands) from 1954 to approximately 1967 to create its own covert listening devices based on a dipole antenna with a detector diode and a small microphone amplifier. The devices were developed under the Easy Chair research contract [8] and were known as Easy Chair Mark I (1955), Mark II (1956), Mark III (1958), Mark IV (1961) and Mark V (1962). [9] Although initially they could not get the resonant cavity microphone to work reliably, several products involving Passive Elements (PEs) were developed for the CIA as a result of the research. In 1965, the NRP finally got a reliably working pulsed cavity resonator, but by that time the CIA was no longer interested in passive devices, largely because of the high levels of RF energy involved. [10]

In May 1960, The Thing was mentioned on the fourth day of meetings in the United Nations Security Council, convened by the Soviet Union over the 1960 U-2 incident where a U.S. spy plane had entered their territory and been shot down. The U.S. ambassador Henry Cabot Lodge Jr. showed off the bugging device in the Great Seal to illustrate that spying incidents between the two nations were mutual and to allege that Nikita Khrushchev had magnified this particular incident as a pretext to abort the 1960 Paris Summit. [11] [12]

See also


  1. Hacking Exposed Linux: Linux Security Secrets & Solutions (third ed.). McGraw-Hill Osborne Media. 2008. p. 298. ISBN   978-0-07-226257-5.
  2. Glinsky, Albert, Theremin: Ether Music and Espionage, University of Illinois Press, Urbana, 2000
  3. George F. Kennan, Memoirs, 1950–1963, Volume II (Little, Brown & Co., 1972), pp. 155, 156
  4. Brown(?), Robert. M. (1967). "Electronic Eavesdroping". Electronics World. Ziff-Davis Publishing Company. 77 (3–6): 23. Retrieved 24 September 2013.
  5. "Design How-To: Eavesdropping using microwaves – addendum". EE Times ( United Business Media. 12 November 2005. Retrieved 24 September 2013.
  6. Pursglove, S. David (1966). "Great Seal Bug". Electronic Design. Hayden Publishing Company. 14 (14–17): 35. Retrieved 24 September 2013.
  7. 1 2 3 4 Murray, Kevin. "THE GREAT SEAL BUG STORY". CounterEspionage. Retrieved January 10, 2016.
  8. "Easy Chair". Crypto Museum. 2 July 2017.
  9. "Easy Chair covert listening devices". Crypto Museum. 30 March 2017.
  10. "Pulsed Cavity Resonator". Crypto Museum. 30 March 2017.
  11. United Nations Security Council Verbatim Report860. S/PV.860 page 15. 26 May 1960. Retrieved 2008-08-29.
  12. Maurits Martijn (24 September 2015). "Operatie Leunstoel: hoe een klein Nederlands bedrijf de CIA hielp om de Russen af te luisteren" (in Dutch). De Correspondent.

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