Sonar-based measurement of user presence and attention

We describe a technique to detect the presence of computer users. This technique relies on sonar using hardware that already exists on commodity laptop computers and other electronic devices. It leverages the fact that human bodies have a different effect on sound waves than air and other objects. We conducted a user study in which 20 volunteers used a computer equipped with our ultrasonic sonar software. Our results show that it is possible to detect the presence or absence of users with near perfect accuracy after only ten seconds of measurement. We find that this technique can differentiate varied user positions and actions, opening the possibility of future use in estimating attention level.