Leon Theremin invented his famous touchless instrument while researching proximity sensors for the Soviet government. He noticed that as his hand moved toward a high-frequency radio oscillator, the interference created an audible squeal that changed pitch with his movement. Recognizing its musical potential, he demonstrated it to Vladimir Lenin, who was so impressed he began taking lessons. The theremin remains the only instrument played without any physical contact, relying on the capacitance of the human body to alter electromagnetic fields around two antennas.