n the project video, a finger swipes and pokes at skin like it’s a touchscreen. As the finger navigates a hairy forearm, a cursor reacts to the movement on the smartwatch screen. There’s no projection and little lag between the finger’s movement and movement on the screen.[…] the researchers developed a ring that sends a high-frequency alternating-current signal into your finger. When your finger touches or hovers above your arm, that signal propagates outward along your skin to a wristband embedded with electrodes. By measuring something called phase difference, which this technology does by comparing the times at which the oscillating signal arrives at two pairs of electrodes, SkinTrack can determine the position of your finger with impressive accuracy.

Source: SkinTrack Turns Your Arm Into a Touchpad. Here’s How It Works