http://www.acm.org/sigchi/chi97/proceedings/paper/fkm.htm

A really wearable input device “FingeRing” is developed for coming wearable PDAs. By attaching ring shaped sensors on each finger, many commands or characters can be input by finger-tip typing action. “FingeRing” can be used on any typing surface such as a knee or desk, so quick operation is realized in any situation while standing or walking. To improve wearability, a very small, ultra low power wireless transmitter is developed that uses the human body as part of an electric circuit. “Direct Coupling” method enables stable communication even when body contacts any grounded surface. A new symbol coding method that combines order and chord typing is also proposed, and useful typing patterns are chosen by typing speed evaluations. Expert users of musical keyboards can input 52 different symbols at speeds of over 200 symbols per minute by using the combination of FingeRing and the new coding method.