yeh, it's of popular belief that it's a theremin that's heard in "good
vibrations."  truth is, it merely mimics a theremin.  you see, the
tannerin (built in the 1950s, by paul tanner) has fixed reference points on a
dummy keyboard so the musician knows exactly where notes can be found, and
produces similar sounds that were before, only unique to the theremin (built in
1919, by lev termen).  but, then, of course, after the theremin, and before
the tannerin, the ondes martenot was built (in the late
1920s, by lev termen and maurice martenot), which is also often confused with
the theremin.  you can hear the ondes martenot being played in radiohead's
song, "the national anthem," on the album, "kid a."  after all these years,
tho, there is still no instrument other than the theremin that can be played
without touching.  the theremin is 'til this day, the only
"space-controlled" instrument.  you have to imagine where the notes are,
and depending on the person and where you are standing in relation to the
instrument, the notes will always be in a different spot each time.