From researcher Kei Nakatsuma at the University of Tokyo Department of Information Physics and Computing comes a new touch based input system using the back of the hand. The wrist mounted device can detect a 2D position of an input device. Nakatsuma stated, "The advantage for using the back of your hand is that your skin can provide haptic feedback." In other words, this same device can detect other types of gestures such as and input, swipe, or drag command.
The device houses a row of infrared detectors that are used to detect the 2D input(s) at a certain distance. (Although this device was not demonstrating multiple input tracking, other systems using a similar array of IL trackers have.) Also in the wrist mounted device are a set of piezoelectric sensors that can be used for the other input gestures by measuring sound. As one taps or drags a finger along the surface near the sensors, a spike or intensity of sound can be seen on a oscilloscope.
In many cases IR sensors fail to function properly. Even though the row of sensors is an easy part of the input process, I think Nakatsuma should focus more on the sound detection. With a row of the same "sound detecting" sensors, a 2D position could be estimated along with all the gestures it can handle. I am only saying this not to squash further infrared research, but the tech has been done many times before and is commercially available. Sound/vibration only input in this area is not.