You shouldn’t be surprised by the revelation that police departments across the country are gathering data about innocent people’s movements.

Using automated scanners, law enforcement agencies across the country have amassed millions of digital records on the location and movement of every vehicle with a license plate, according to a study published Wednesday by the American Civil Liberties Union. Affixed to police cars, bridges or buildings, the scanners capture images of passing or parked vehicles and note their location, uploading that information into police databases. Departments keep the records for weeks or years, sometimes indefinitely.

The ACLU study is here.

You should be outraged that your tax dollars are going into surveillance that undercuts your privacy, but don’t be surprised. Why not? Because Cato told you so.

Here’s text from a study we published nearly nine years ago, Understanding Privacy—and the Real Threats to It:

Red-light cameras and speed cameras are another part of the rapidly growing Big Brother infrastructure. Little technical difference separates a digital camera that takes occasional snapshots from one that records continuous footage. Equipped with optical character recognition technology, traffic cameras may soon have the technical capability to read license plates and scan traffic for specific cars. Networked cameras will be able to track cars throughout a city and on the highways. And database technology will make it possible to create permanent records of the movements of all cars captured on camera.

That material is based on testimony I gave to the House Transportation and Infrastructure Committee’s Subcommittee on Highways and Transit almost a dozen years ago. In it, I addressed the constitutional status of public monitoring like this. I talked about how license plates deprive drivers of the ability to navigate streets anonymously. That’s not the worst privacy invasion, given how driving laws and traffic disputes are administered. But it’s akin to requiring people to wear nametags to walk on public sidewalks.

Because the law has deprived people of the ability to protect privacy, the better view is that there is a Fourth Amendment search when law enforcement notes the license plates on cars. This search is inherently unreasonable if they do so when they do not suspect crime. As soon as red-light cameras are used for anything other than snapping suspected speeders — and they soon will be — these cameras should be shown a red light themselves.

Courts have only just begun to grapple with these issues, including the Supreme Court in the Jones case, which last year held that the government couldn’t attach a GPS device to a car and monitor its movements, even in public, without getting a warrant. I wrote about the state of Fourth Amendment law in this area in an article cleverly (ahem) titled: “U.S. v. Jones: Fourth Amendment Law at a Crossroads.”

Concerned? Yes, you should be. Angry? If you need that outlet. But don’t be surprised to learn that police departments are tracking of every car’s movements without a warrant.