Theremin recalled that while still in his last year of school, he had built a million-volt Tesla coil and noticed a strong glow associated with his attempts to ionize the air.

A chance meeting with Abram Fedorovich Ioffe led to a recommendation to see Karl Karlovich Baumgart, who was in charge of the physics laboratory equipment.

Abram Fedorovich suggested Theremin also look at methods of creating gas fluorescence under different conditions and of examining the resulting light's spectrum.

[citation needed] In the course of the next three and a half years he oversaw the construction of a radio station in Saratov to connect the Volga area with Moscow, graduated from Petrograd University, became deputy leader of the new Military Radiotechnical Laboratory in Moscow, and finished as the broadcast supervisor of the radio transmitter at Tsarskoye Selo near Petrograd (then renamed Detskoye Selo).

[6] During the Russian Civil War, in October 1919 White Army commander Nikolai Nikolayevich Yudenich advanced on Petrograd from the side of Detskoye Selo, apparently intending to capture the radio station to announce a victory over the Bolsheviks.

[7] Theremin recalled that on an evening when his hopes of overcoming these obstructing experts reached a low ebb, Abram Fedorovich Ioffe telephoned him.

[8] Ioffe asked Theremin to come to his newly founded Physical Technical Institute in Petrograd, and the next day he invited him to start work at developing measuring methods for high-frequency electrical oscillations.

[9] He built a high-frequency oscillator to measure the dielectric constant of gases with high precision; Ioffe then urged him to look for other applications using this method, and shortly made the first motion detector for use as a "radio watchman".

[note 1][10][11] While adapting the dielectric device by adding circuitry to generate an audio tone, Theremin noticed that the pitch changed when his hand moved around.

[19] After being sent on a lengthy tour of Europe starting 1927–including London, Paris, and towns in Germany[14][20] – during which he demonstrated his invention to full audiences, Theremin went to the United States arriving on 30 December 1927 with his first wife Katia.

Afterwards, while working with the American Negro Ballet Company, the inventor married a young African-American prima ballerina Lavinia Williams.

Although rumors of his execution were widely circulated and published, Theremin was put to work in a sharashka (a secret laboratory in the Gulag camp system), together with Andrei Tupolev, Sergei Korolev and other well-known scientists and engineers.

A precursor to the modern laser microphone, it worked by using a low-power infrared beam from a distance to detect sound vibrations in glass windows.

[2][34] Lavrentiy Beria, the head of the secret police organization NKVD (the predecessor of the KGB), used the Buran device to spy on the British, French and US embassies in Moscow.

Theremin invented another listening device called The Thing, hidden in a replica of the Great Seal of the United States carved in wood.

It hung in the ambassador’s residential office in Moscow and intercepted confidential conversations there during the first seven years of the Cold War, until it was accidentally discovered in 1952.

[40] In the 1970s, Leon Theremin was a Professor of Physics at Moscow State University (Department of Acoustics) developing his inventions and supervising graduate students.

After 51 years in the Soviet Union Theremin started traveling, first visiting France in June 1989[2] and then the United States in 1991, each time accompanied by his daughter Natalia.

In 2022, French writer Emmanuel Villin published the novel La Fugue Thérémine (éditions Asphalte), which looks back on the life of Leon Theremin.