Belinda's brain

 I found  Leon Theremin playing this instrument over on YouTube and I thought it was some kind of a quirky joke but with further reading I not only discovered that it's a real instrument (they sell 'em over on EBay) but that they've  been used in songs we've all heard before. It's been suggested that you forgo trying  to make your own theremin from scratch because they carry an extremely  high voltage and you could very likely kill yourself.

Leon Theremin

 Theremin invented a device called the thing and it was used by the Soviet Union to spy on the United States. The device was embedded in a carved wooden plaque of the Great Seal of the United States and on August 4, 1945, a delegation from the Young Pioneer organization of the Soviet Union presented the bugged carving to U.S. Ambassador Averell Harriman, as a "gesture of friendship" to the USSR's World War II ally.

It hung in the ambassador’s Moscow residential study until it was exposed in 1952 during the tenure of Ambassador George F. Kennan. The existence of the bug was accidentally discovered by a British radio operator who overheard American conversations on an open radio channel as the Russians were beaming radio waves at the ambassador's office. The Department of State found the device in the Great Seal carving after an exhaustive search of the American Embassy, and Peter Wright, a British scientist and former MI5 counterintelligence officer, eventually discovered how it worked. Assuming that the device had never been discovered, it could easily have worked for 50 years or more.

*Source

Some of Theremin's inventions

Theremin – the classic Theremin (1920)
Burglar alarm, or "Signalling Apparatus" which used the Theremin effect (1920s)
Electromechanical television – Nipkow disk with mirrors instead of slots (ca. 1925)
Terpsitone – platform that converts dance movements into tones (1932)
Theremin cello – an electronic cello with no strings and no bow, using a plastic fingerboard, a handle for volume and two knobs for sound shaping (ca. 1930)[31][32][33][34]
Theremin keyboard – a piano-like device (ca. 1930)
Rhythmicon – world's first drum machine (1931)
The Buran eavesdropping device (1947 or earlier)
The Great Seal bug, also known as "The Thing" – one of the first passive covert listening devices; first used by the USSR for spying (1945 or earlier)
His invention of "The Thing", an espionage tool, is considered a predecessor of RFID technology.