If you drive through Maryland, the state may be using an automated reader to photograph your license plate — and storing your movements away for future use. Maryland is not alone. ACLU offices in 38 states are looking into how the government is using license-plate readers across the country — and what it is doing with the data. The ACLU is already calling the license-plate readers “the next big thing in government tracking.”

There are some uses of automatic license-plate readers that most people would agree are relatively unobjectionable — looking for cars that fled crime scenes or have been stolen, for example. The real problem is that when the government stores that information, it is not trying to solve an ongoing crime — it is building a database. These databases can quickly fill up with all sorts of details about how people lead their lives. By piecing together the locations of a particular license plate over time, the government may be able to determine if someone goes to church, synagogue or mosque regularly; whether they go to meetings of a particular political group; whether they participate in protests; or even if they are having an affair.

It’s hard to know how widespread the technology is, but to give one example, Los Angeles County alone is using hundreds of license-plate readers. According to LA Weekly, which got its numbers in part through public-records requests, Los Angeles police have recorded more than 160 million data points about the movements of millions of drivers.

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