The ACLU found that only five states have laws governing license plate readers. New Hampshire, for example, bans the technology except in narrow circumstances, while Maine and Arkansas limit how long plate information can be stored.

“There’s no expectation of privacy” for a vehicle driving on a public road or parked in a public place, said Lt. Bill Hedgpeth, a spokesman for the Mesquite Police Department in Texas, which has records stretching back to 2008, although the city plans next month to begin deleting files older than two years. “It’s just a vehicle. It’s just a license plate.”

In Yonkers, New York, police said retaining the information indefinitely helps detectives solve FUTURE CRIMES. In a statement, the department said it uses license plate readers as a “reactive investigative tool” that is only accessed if detectives are looking for a particular vehicle in connection to a crime.

“These plate readers are not intended nor used to follow the movements of members of the public,” the department’s statement said.

But even if law enforcement officials say they don’t want a public location tracking system, the records add up quickly. In Jersey City, New Jersey, for example, the population is only 250,000 but the city collected more than 2 million plate images on file. Because the city keeps records for five years, the ACLU estimates that it has some 10 million on file, making it possible for police to plot the movements of most residents depending upon the number and location of the scanners, according to the ACLU.

The ACLU study, based on 26,000 pages of responses from 293 police departments and state agencies across the country, also found that license plate scanners produced a small fraction of “hits,” or alerts to police that a suspicious vehicle has been found. .