Smartwatches Can Now Track Your Finger in Mid-Air using sonar

As mobile and wearable devices such as smartwatches grow smaller, it gets tougher for people to interact with screens the size of a matchbook. That could change with a new sonar technology developed by University of Washington computer scientists and electrical engineers that allows you to interact with mobile devices by writing or gesturing on any nearby surface — a tabletop, a sheet of paper or even in mid-air.