The time-sensitive pattern created by that pinch-circle motion, along with the motion involved in rotating the dial, are complex enough that Memon says a study of about 100 users has shown it can identify users with about 2% false positives and 2% false negatives.
In one of its most sensitive police "pattern or practice" investigations to date, the Justice Department is now working to get Los Angeles city officials to sign a consent decree authorizing a third party to monitor the city's Police Department and imposing other safeguards.