It was invented around the 1920s, and the inventor, Léon Theremin -- he also was a musician besides an inventor -- he came up with the idea for making the theremin, I think, when he was working on some shortwave radios.
Fu inventato intorno agli anni '20. L'inventore del theremin, Léon Theremin, è stato sia un musicista che un inventore. L'idea del theremin gli è venuta mentre lavorava sulle radio ad onde corte.