The theremin is perhaps one of the earliest electric instruments ever made. It consists of a main body with two antenna, one vertical and the other horizontal and looped on the end. The vertical antenna controls pitch, while the horizontal one volume. It is played by holding your hands in the air close to, but not touching the antenna. The closer your hands are to the antenna, the higher or softer the note is, vice versa.
The sound it produces is a warbly, eerie cross between violin and flute, allowing it to shock an audience with it's unusually beautiful tone when played right. It translates hand position into sound through oscillators that use the antenna as their plate. The electric signals are passed through filters and amplified by the theremin and usually put through a loudspeaker.