You know the Beach Boys song "Good Vibrations"?

You know that weird, eerie sound that floats through the song? That's a theremin, or at least a synthesized version of one.

A thermin is basically a box with one vertical antenna sticking out the top and another, circular antenna sticking out the side. When you turn it on, it creates a tone. Then, by moving yours hands closer to and farther away from the antennas, you can vary the pitch and volume of the tone.

How does it work?

It combines two high frequency radio signals and conducts them through the antennas to produce the tone. When I move my hands near the antenna my body becomes part of the electrical circuit and changes its frequency. It's kind of like how you can affect the reception of your TV or radio depending on where you stand near it. If you do it right the theremin can produce some pretty spooky sounds. In fact, it was used a lot in sci-fi and horror movies.

It never really caught on as a widely used instrument, but it did give rise to synthesizers and other electronic instruments.