If you've never seen a theremin, you're not missing too much, but it is legit kind of cool. First, just take a goosey gander at one:
Yep, even Moog has made one. Does it lend it any more street-cred? About as much as if Ibanez started making accordians. Which is to say, no. But don't get me wrong, you've got to at least see a video of someone playing it, so when some goofy nerd guy says "Hey, have you ever heard of a theremin?" you can be like "Yeah, bro, of course, duh." But don't admit that was the first time you learned how to pronounce it.
You can watch this video of this guy playing Over the Rainbow on one, or just open any video of a cat sitting on a fence shrieking all night.
So the way it works is witchcraft. You don't even touch it. The loopty-loop antenna controls the volume and the vertical one controls the pitch. It's invention was funded by the Soviet government in 1920, where this physicist named Lev Sergeevich Termen (Theremin) was doing research with proximity sensors. He eventually bailed on Russia after their civil war and got a patent in the states.
I'm guessing it's in the public domain at this point, because you can buy kits to build your own, or go to Radio Shack and buy the parts following this chart:
Don't blame me if this thing hacks your wi-fi password or something. I don't trust it any more than I do the wizardry of Tesla coils.