Nokia Research Labs has created a magnetic ring called Nenya, after Galadriel's Ring of Power, that can control your cellphone as you twist it on your finger.
The magic behind this functionality isn't really all that magical: by mounting a magnet on a ring, you can create a magnetic field with a detectable orientation. As you twist the ring around your finger, that orientation changes, which functions as an analog input dial of sorts.
A Bluetooth-equipped bracelet picks up on the field orientation, and by tugging the ring forward on your finger a bit, you've effectively got a 'select' button. All these inputs are sent to your cellphone, enabling you to do everything from toggling your music to answering calls to interacting with specialized apps.
In user testing, Nokia has found that most people can accurately position the ring in increments of 45 degrees, suggesting that eight different options could exist on one ring, or more if you're willing to move the ring back and forth along the axis of your finger. And while the sensor bracelet is pretty fugly at the moment, there's no reason the technology couldn't be built into something like a watch. Or for that matter, just kill two birds with one stone and put the phone in the watch too. Problem solved!