“Where someone goes can reveal a great deal about how he chooses to live his life,” Catherine Crump, a law professor at the University of California, Berkeley, told Ars. “Do they park regularly outside the Lighthouse Mosque during times of worship? They’re probably Muslim. Can a car be found outside Beer Revolution a great number of times? May be a craft beer enthusiast—although possibly with a drinking problem.”

In August 2014, the American Civil Liberties Union and the Electronic Frontier Foundation lost a lawsuit to compel the Los Angeles Police Department and the Los Angeles Sheriff’s Department to hand over a mere week’s worth of all LPR data. That case is now on appeal.

In Oakland, OPD’s current LPR dataset shows only a few data points for most vehicles. But there are exceptions—such as the car seen 459 times over two years on a certain block of Chabot Road, east of the Rockridge BART station (one of the city’s richer areas). As Oakland and cities like it deploy more LPR cameras, such datasets could quickly grow more complete.

“Project forward to a world where LPR technology is cheap and they can be mounted on every police car and posted at every traffic light,” said Crump. “Do you think that anyone with a badge should be able to search through that data at their discretion? If not, then you should support restrictions on how long law enforcement agents can store this data, and who can access it, and under what circumstances.”