Smart devices just got even smarter.

• Position: Technology

As mobile and wearable devices such as smart-watches 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 computer scientists and electrical engineers at the University of Washington, Seattle, that allows users to interact with mobile devices by writing or gesturing on any nearby surface--a tabletop, a sheet of paper, or even in mid air.

FingerIO tracks fine-grained finger movements by turning a smartphone or smartwatch into an active sonar system using the device's own microphones and speakers. Because sound waves travel through fabric and do not require a line-of-sight, users even can interact with a phone inside a front pocket or a smartwatch hidden under a sweater sleeve. FingerIO accurately can track two-dimensional finger movements to within eight millimeters, which is sufficiently accurate to interact with today's mobile devices.

"You can't type very easily onto a smartwatch display, so we wanted to transform a desk or any area around a device into an input surface," explains Rajalakshmi Nandakumar, a doctoral student in computer science and engineering. "I don't need to instrument my fingers with any other sensors--I just use my finger to write something on a desk or any other surface and the device can track it with high resolution."

Using FingerIO, one could use the flick of a finger to turn up the volume, press a button, or...