...Ever seen a 50’s SF movie and heard an eerie sound in the score that somehow did and didn’t fit in with the orchestra?

“The day the Earth stood still” ... (Klaatu Baradu Niktu) Hitchcock’s  “Spellbound” theme... or possibly even the original “Startrek” theme?

Chances are you heard a THEREMIN. 

A wailing ethereal sound; the player doesn’t touch the instrument while playing. The perfect musical illustration for flying saucers, mental disorder, or things going horribly wrong.

                                    the master in action!

see: http://www.youtube.com/watch?v=w5qf9O6c20o&feature=related

...the theremin played by the inventor Lev Sergeyevich Thermen himself!