Tracking People from Smartphone Accelerometers

It's been long known that individual analog devices have their own fingerprints. Decades ago, individual radio transmitters were identifiable and trackable. Now, researchers have found that accelerometers in smartphone are unique enough to be identifiable.

The researchers focused specifically on the accelerometer, a sensor that tracks three-dimensional movements of the phone ­ essential for countless applications, including pedometers, sleep monitoring, mobile gaming ­ but their findings suggest that other sensors could leave equally unique fingerprints.
"When you manufacture the hardware, the factory cannot produce the identical thing in millions," Roy said. "So these imperfections create fingerprints."
Of course, these fingerprints are only visible when accelerometer data signals are analyzed in detail. Most applications do not require this level of analysis, yet the data shared with all applications -- your favorite game, your pedometer -- bear the mark. Should someone want to perform this analysis, they could do so.
The researchers tested more than 100 devices over the course of nine months: 80 standalone accelerometer chips used in popular smartphones, 25 Android phones and two tablets.
The accelerometers in all permutations were selected from different manufacturers, to ensure that the fingerprints weren't simply defects resulting from a particular production line.
With 96-percent accuracy, the researchers could discriminate one sensor from another.