The Theremin is one of the most unique musical instruments in existence because it is played without any physical contact. It was invented by Russian physicist Leon Theremin in 1920. The instrument consists of two metal antennas that sense the relative position of the player's hands. One hand controls the frequency (pitch) while the other controls the amplitude (volume). Electric signals from the theremin are amplified and sent to a loudspeaker. It was originally the product of Russian government-sponsored research into proximity sensors. The theremin has a distinct, eerie sound that became a staple in early science fiction film soundtracks and was later used by rock bands like The Beach Boys and Led Zeppelin. It remains a challenging instrument to master due to the lack of tactile feedback for the performer.