Your Phone’s Tilt Sensor Can Identify You

The sensor that lets your phone know which way the screen is oriented also—thanks to minute manufacturing variations—emits a unique data “fingerprint” that could allow your phone to be tracked, even if all other privacy settings are locked down, researchers say.

In addition to governing basic things like screen orientation, accelerometer data is widely used by apps such as pedometers and mobile games. Meanwhile, many apps often rely on advertising, which has led advertisers to search for ways to track users and their Web habits.

Even if you don’t allow apps to see your personal data or location, just the raw movements of the phone—which can be measured without permission—can betray the phone’s unique identity and track it over time, says Romit Roy Choudhury, an associate professor at the University of Illinois who cowrote a paper with colleagues at the University of South Carolina that describes the phenomenon. “There has been a lot of work to catch the leakage of ID information from phones,” he says. “We are now saying that accelerometer data going out of the phone can be treated as an ID.”
Accelerometers use a technology called micro-electro-mechanical systems, or MEMS. In the case of an accelerometer, tiny bars of metal move between other metal bars in response to motion, changing electrical capacitance and indicating 3-D movement. Using this information, a smartphone can determine a change in screen orientation, or translate physical movements to a character in a game.
But the underlying data varies minutely from accelerometer to accelerometer, the researchers found. After testing 80 accelerometer chips—plus 25 Android phones and two tablets that used accelerometers—the researchers could pick out the fingerprint with 96 percent accuracy.