FingerIO:
"FingerIO is a novel fine-grained finger tracking solution that transforms any space around off-the-shelf smartphones or smartwatches into an interactive surfaces. FingerIO does not require instrumenting the finger with sensors and works even in the presence of occlusions between the finger and the device. We achieve this by transforming the device into an active sonar system that transmits inaudible sound signals and tracks the echoes of the finger at its microphones."
