If you've ever heard the eerie electronic music at the beginning of a 1950s science fiction movie (The Day the Earth Stood Still, for example), then you've heard a theremin. Invented in Russia in the 1920s, the instrument is unique, in that the person playing it doesn't touch it at all. Instead, they move their hands around its two antennas, causing it to emit different sounds by altering radio frequencies that the machine emits. Although still used by some modern musicians, theremins can be a little pricey, and somewhat difficult to master. That's where the $35 Beep-It optical theremin comes in.
The Beep-It emits a square sound wave, the pitch of which is controlled by the amount of light striking a built-in photoresistor. Users can alter the pitch by shading the light sensor, pointing it towards a light source, or even bringing a bright light source up to it. Flashing lights, such as a bicycle tail light, will produce a spacey oscillating sound. A prominent power button allows users to repeatedly turn it quickly on and off, which can be an interesting effect in itself. It also has a basic volume control.
Although it looks like a toy, the Beep-It does incorporate a quarter-inch output jack, so it can be connected to things like amplifiers or recording devices. As can be seen in the video below, it could find a place with some bands, especially those of the more psychedelic persuasion.
Made by Chicago-based electronics tinkerers Unatronics, the Beep-It optical theremin is available on the company website for US$35. It requires one 9-volt battery.