The Gift That Listened: How a Soviet Bug With No Battery Spied on America’s Ambassador

On August 4, 1945, with the war in Europe over and the war in the Pacific days from its end, a group of Soviet schoolchildren from the Young Pioneers arrived at the residence of the American ambassador in Moscow bearing a gift. It was a large, hand-carved wooden plaque of the Great Seal of the United States: the eagle, the shield, the arrows and olive branch, all polished to a rich glow. The ambassador, W. Averell Harriman, accepted it as a gesture of friendship between wartime allies and had it hung on the wall of his study.

It stayed there for seven years, through four ambassadors. And for much of that time, whenever the Soviets wanted to, they could hear every word spoken in the room. Hidden inside the carving was a listening device unlike anything Western security men had seen: no battery, no wires, no tubes, nothing to wear out and nothing that gave off a signal of its own. When American technicians finally pried it loose in 1952 they were so baffled by how it worked that they gave it the only name that seemed to fit. They called it “The Thing.”

Its designer was a man the American public already knew, though not as a spy. He was Leon Theremin, the inventor of the eerie electronic instrument you play by waving your hands in the air.

The man who made music out of thin air

Lev Sergeyevich Termen was born in St. Petersburg in 1896 and trained as a physicist and radio engineer. In 1920, working at Abram Ioffe’s new Physical Technical Institute in Petrograd, he built a high-frequency oscillator to measure how gases affect an electric field. When he added a circuit to turn the readings into an audible tone, he noticed that the pitch changed as his hand moved near the apparatus. His body was acting as one plate of a capacitor, and moving it detuned the circuit.

Termen, who played the cello, turned the accident into an instrument. A modern theremin has two metal antennas: bring one hand closer to the vertical rod and the note rises; move the other toward the horizontal loop and the volume drops. Inside, two radio-frequency oscillators run at almost the same frequency, and the player’s hand shifts one of them slightly. The difference between the two, the “beat,” falls in the range of human hearing and comes out of the speaker as a singing, wavering tone.

By the late 1920s the inventor, now billed as Leon Theremin, was a sensation. He toured Europe to packed halls, arrived in New York in December 1927, played with the New York Philharmonic, patented the instrument in the United States in 1928 and licensed it to RCA. He set up a laboratory in Manhattan, built a metal detector for Alcatraz, worked with the virtuoso Clara Rockmore and married a young ballerina, Lavinia Williams. Then, in 1938, he vanished. He had sailed home to the Soviet Union, leaving debts and rumors behind. Whether he left out of homesickness, money trouble or something more sinister is still argued over.

At home he was arrested in Stalin’s purges, held in Moscow’s Butyrka prison and sent to the Kolyma gold fields in the Far East. Eventually the state found a better use for him. He was moved to a sharashka, one of the secret prison laboratories where jailed scientists and engineers, among them the aircraft designer Andrei Tupolev and the future rocket chief Sergei Korolev, worked on projects for the security services. There Theremin built eavesdropping equipment, including an infrared system called Buran that could pick up speech from the vibrations of a window pane, an ancestor of today’s laser microphone. It won him a Stalin Prize in 1947. He also built The Thing.

A gift for the ambassador

The Soviet Union had good reason to want ears inside Spaso House, the grand 1913 mansion that has served as the American ambassador’s residence since the 1930s. Harriman had attended the great wartime conferences with Roosevelt, Churchill and Stalin, and the ambassador’s study was where much of America’s thinking about the Soviet Union got talked through. In 1947 Secretary of State George Marshall used the same room as a temporary office during a foreign ministers’ conference in Moscow.

A carved Great Seal was a clever choice of Trojan horse. No diplomat would refuse a children’s gift honoring his own country, and no ambassador was likely to stuff the national emblem in a closet. It went up on the wall and stayed there while Harriman gave way to Walter Bedell Smith, then Alan Kirk, then George Kennan.

How a bug with no battery works

The heart of The Thing was a small copper cylinder, about the size of a thimble, with a polished silver-plated interior. One end was closed by a conductive membrane so thin and fragile that it was damaged when the Americans first handled it. Behind the membrane, almost touching it, sat a flat, mushroom-shaped tuning post. A straight antenna about 9 inches (23 centimeters) long poked out of the side. The whole assembly weighed roughly an ounce, and it was mounted in a hollowed-out space just beneath the eagle’s beak. Accounts differ on whether tiny holes were drilled to let the sound in, or whether the wood there was simply thin enough to pass it.

On its own, the device did nothing at all. It came alive only when someone outside aimed a strong radio beam at the building, a trick the U.S. National Security Agency calls “illuminating” a target. The antenna caught the beam and fed it into the cylinder, which was built to resonate at that frequency, much as a wine glass rings at one particular note. The resonating cavity then sent a faint copy of the beam back out through the antenna.

The clever part was the membrane. When someone spoke in the study, sound waves pressed on the thin metal skin, shifting it ever so slightly toward or away from the tuning post. Membrane and post together formed a tiny capacitor, so every word changed the capacitance, which nudged the cavity’s tuning, which in turn changed the strength of the reflected signal. In other words, the room’s conversation was stamped onto the echo as ordinary amplitude modulation, the same scheme used by AM radio. A listening post nearby, in a neighboring building or perhaps a parked car, picked up the echo and turned it back into speech.

It is the theremin’s principle turned inside out. In the instrument, a moving hand changes a capacitance and so changes a radio-frequency circuit, and the change becomes sound. In the bug, sound moves a membrane, changes a capacitance and so changes a radio signal. The idea of a vibrating surface carrying information would have pleased Ernst Chladni, whose sand-covered plates made sound visible more than 150 years earlier.

Because the bug had no power source and transmitted nothing until it was illuminated, a security sweep at the wrong moment would find only a block of wood. It could never run down. Exactly which frequency the Soviets used is one of the story’s lingering puzzles. Published accounts over the years, including one traced to the British engineer Peter Wright, who studied the device and later wrote the memoir Spycatcher, gave figures from about 330 to 800 megahertz. But the FBI’s 1952 laboratory report, declassified in 2019, put its resonance at around 1,700 megahertz and found that it sent back the same frequency it received.

Seven years of listening, and a hunt

Western officials had long assumed that the walls in Moscow had ears, but finding them was another matter. In 1951 a British radio operator monitoring Soviet air force channels suddenly heard the British air attaché’s voice coming through his receiver loud and clear. Not long afterward an American heard what sounded like a conversation from the ambassador’s residence. A State Department security team, John Ford and Joseph Bezjian, searched Spaso House and found nothing. Whatever was there, its operators had apparently switched off the beam before the sweep began.

In September 1952 Bezjian came back with a better plan. Instead of arriving as an obvious technician, he posed as a house guest. His equipment was smuggled in ahead of him by the embassy’s resident personnel officer, Sam Janey, and locked in a safe. Kennan, the new ambassador and one of the few people in on the scheme, then summoned his secretary in the evening and dictated a dummy dispatch, giving any eavesdroppers a reason to switch on.

They took the bait. Sweeping the study with a simple broadband receiver, Bezjian picked up the ambassador’s own voice coming back at him from the air. The signal seemed to come from the wall behind the Great Seal. When he took the carving down, the signal disappeared from the wall. The bug was inside the gift itself. Bezjian found that the plaque could be opened, pulled out the little cylinder and its antenna, and reportedly slept with it under his pillow that night so no one could steal it back.

The device was flown to Washington, where the Secretary of State showed it to President Truman. Truman ordered the FBI to work out how it functioned and the Naval Research Laboratory to build detectors for others like it. The FBI’s technicians borrowed microwave test gear from the National Bureau of Standards because their own equipment did not reach high enough frequencies. By December 1952 they had a full technical report and two working copies.

Kennan’s own stay in Moscow ended within weeks. Frustrated by the isolation and the plainclothes police who followed him everywhere, he told reporters during a stop in Berlin that life in the residence reminded him of his internment by the Nazis in 1941 and 1942. Moscow declared him persona non grata and refused to let him return. He later called the remark “a foolish thing for me to have said.”

Copying the Thing

The discovery was kept quiet, but it rippled through the world’s intelligence services. The British were brought in, and Wright, then working with the Marconi company, built a British version under the code name SATYR, which was used through the 1950s by Britain, the United States, Canada and Australia. The CIA paid the Dutch radar laboratory in Noordwijk to develop its own passive bugs under a program called EASY CHAIR, which ran from 1954 until about 1967. By the time the Dutch had a reliable cavity microphone, the CIA had lost interest, partly because illuminating one took so much radio power.

The concept was not entirely new. An RCA engineer, Winfield Koch, had filed a U.S. patent on a resonant cavity microphone in 1941. But nobody in the West had thought to use the idea to build a bug that could sit in a wall for years.

“It was right under the beak of the eagle”

For eight years the American public knew almost nothing about The Thing. Then, on May 1, 1960, the Soviets shot down Francis Gary Powers’s U-2 spy plane, and Moscow called a meeting of the United Nations Security Council to denounce American espionage. On the fourth day, May 26, the U.S. ambassador to the U.N., Henry Cabot Lodge Jr., produced a wooden Great Seal, opened it in front of the cameras and showed the delegates the device hidden inside. (The CIA later said the piece Lodge displayed was a replica.) Spying, he argued, went both ways, and he added that more than 100 hidden microphones had been found in U.S. embassies and residences in the Soviet bloc. The Soviet resolution condemning the United States was defeated 7 votes to 2, with only Poland siding with Moscow.

The show was a Cold War moment as theatrical as anything in the era, and it fits a long tradition of machines with something hidden inside, from the Mechanical Turk, whose cabinet concealed a human chess master, to the CIA’s own audacious attempt to lift a Soviet submarine off the Pacific floor. Electronic warfare inside the Moscow embassy did not end with the seal, either. From 1953 to 1976 the Soviets also aimed a low-power microwave beam, later known as the “Moscow Signal,” at the U.S. embassy building, for reasons that were never officially explained.

There is one more irony. In 1951, the year before Bezjian found The Thing, Hollywood released a science fiction film called The Thing from Another World, and its unsettling score featured the theremin.

From spy bug to the tag in your sweater

Theremin himself stayed in Soviet service, working for the KGB until 1966. He later taught at the Moscow Conservatory and at Moscow State University, and in his nineties he was allowed to travel again, visiting France in 1989 and the United States in 1991, where he appeared at Stanford. He died in Moscow in 1993, at 97.

His bug outlived the Cold War in a way he could not have predicted. The Thing is widely regarded as a forerunner of radio-frequency identification, or RFID: a passive device that has no power of its own, wakes up when a reader’s radio wave hits it, and answers by changing how it reflects that wave. In 1973 Mario Cardullo patented a passive radio transponder with memory, and the same year researchers at Los Alamos demonstrated “modulated backscatter” tags at 915 megahertz, the technique most UHF RFID tags still use. Today those descendants ride in toll transponders, library books, building access cards and the price tags of clothing, where they let a store count its stock in seconds.

The difference is that a hotel key card announces itself when asked. The Thing was built never to be noticed at all, and for seven years, in one of the most closely watched houses in Moscow, it wasn’t. In 2025 a veteran counter-surveillance specialist, John Little, built a working replica to show how it was done. It still works the way it did in 1945: you speak, a thin metal skin trembles, and somewhere outside, someone hears you.

The Thing was, in the end, a recorder without a recorder: a way of catching voices in a room and carrying them somewhere else. For a gentler story about capturing speech, see how a jazz fan’s wire recorder became aviation’s black box.

Further reading