Research Group Uses Sonar for Computer Power Management

You're watching a movie on your computer and suddenly the screen goes black, leaving you to wiggle your mouse so you don't miss anything. You get up from your computer to get a snack from the kitchen, and you come back to find your screen still on, leaching power from your laptop's limited battery.

You're at the computer, you're not at the computer: How can your computer know?

Yet when it comes to power management on computers, turning the screen on and off can mean major power savings; screens use up to 40 percent of the computer's power.

A research group at the McCormick School of Engineering and Applied Science at Northwestern University has developed a new way for your computer to detect if you're there, and they're looking for test subjects to try it out and see just how much power it saves.

Their solution? Using your computer's existing hardware — the microphone and speakers — and echolocation to determine whether you're watching a movie (there) or getting a snack (away).

"The idea to work on this problem came from my own experience," says Stephen Tarzia, a computer science graduate student in the Empathic Systems Project headed by electrical engineering and computer science professors Peter Dinda and Gokhan Memik and adjunct professor Robert Dick. "I'm obsessive about saving power. So I tried putting an icon on my task bar that I would click to shut off my screen before I walked away, but I wouldn't remember to click it. I thought about putting a lever on the mouse, but when you're at the computer, you're not always using a mouse."

Discussions among the group led to the idea of using sonar. The group developed software that, when the user is not using the mouse or keyboard, plays a tone at a high frequency and records the tone's echo. The computer then processes the tone and filters out everything except the frequency and looks for variance.

"If the echo is constant over 10 seconds, that tends to indicate there is no one there," Tarzia says. "If there are fluctuations, it's likely due to a person's movements."

The software can detect movements from up to about eight feet away. If it discovers that the user is not there, it turns off the screen, and the sonar isn't reactivated until there is mouse movement.

The group is currently looking for users to download the software and test it to see just how much power it saves. The software logs when the user stops using the mouse and keyboard and logs the results from the sonar. The results, in the form of numbers, are completely anonymous. Researchers don't listen to recordings — they just look at the data from the recordings.

"We're interested in the larger question of saving power in whatever way possible," Tarzia says. "We've proven that this system works, and now we want to see how useful it is. The broad goal is to reduce the power consumed by computers; this would lengthen battery-life, reduce electricity costs, and reduce environmental impacts."

To download the software and participate in the study: