The revelation from the American Civil Liberties Union about the vast extent of license plate tracking and the indefinite retention of millions of sensitive records is the latest in disturbing news for privacy advocates.

Since they're already in public view, collecting information on license plates appears innocuous enough, especially if it’s done by police to investigate criminal activity.

But even if these records are legitimately needed by law enforcement, there’s just no reason to keep the records around for years or even indefinitely.

Some progressive state lawmakers have already approved legislation mandating limits on how long such information can be kept. In Vermont, lawmakers have cut police retention of data from four years to 18 months.

Other state legislatures and local police departments should follow suit with clearly defined policies, so that citizens can at least know the rules of this new privacy game.

Even though automated license plate readers (ALPRs) have been around since at least 2008, many people probably remain entirely in the dark about their widespread use. The revelation only compounds the existing justified dismay about the National Security Agency’s surveillance of phone call data.

Worse, it compounds existing and often less publicized fears about how new digital technologies can infringe on privacy if not properly policed.

Cell phone data can also be used to track your location and is stored by telecommunications companies. Similarly, political controversies late last year over updating electronic privacy laws showed that the rules governing law enforcement access to emails are decades old and often allow access without a warrant.

Most of the time, the government and police have no interest in where you are or what you’re doing. But the courts are a mess, with conflicts between state and federal circuits on all sorts of intricate details of privacy law, often involving the Fourth Amendment and freedom from unreasonable search.

As technologies proliferate, citizens at least need to stay informed and vigilant of where the next blow to privacy could come from.

Maybe we should stay a step ahead, and start filing Freedom of Information Act (FOIA) requests of our own. Then we could watch the watchers watch us.