Who knows?! The constitutionality of license plate readers has yet to be challenged head on. Federal courts have decided that scans by license plate readers are constitutional searches that do not require a warrant because the plates are out in public, plain view and so there is no reasonable expectation of privacy. U.S. v. Diaz-Castaneda, 494 F.3d 1146, (9th Cir. 2007); U.S. v. Ellison, 462 F.3d 557, (6th Cir. 2006); U.S. v. Walraven, 892 F.2d 972 (10th Cir. 1989). However, in Minnesota, license plate readers are statutorily authorized and the data is regulated under Minn. Stat. § 13.824. So the straight, short answer is, yes, license plate readers are legal in Minnesota.
License plate readers are tiny high-speed cameras that photograph thousands of license plates on passing cars every minute. These readers are often mounted on police cars, road signs, and bridges. Information including license plate numbers, the date, time, and location on vehicles, and pictures of license plates, vehicles, and areas surrounding vehicles is captured and cataloged. In Minnesota, such data is only kept for 60 days and may only be used to match with license plate data. Such information may not be used to monitor or track someone under criminal investigation, unless authorized by a warrant or an emergency circumstance where there’s not enough time to obtain a warrant.
Privacy and civil liberty advocates argue that the constant and indiscriminate monitoring and surveillance conducted by license plate readers bypasses the Fourth Amendment, which prohibits unreasonable searches and seizures without a warrant supported by probable cause or some legitimate exception to the warrant requirement. Proponents of license plate readers argue they help take dangerous drivers off the road and help solve crimes.
Until either the Minnesota or U.S. Supreme Court find otherwise, license plate readers are legal in Minnesota. And so it’s legal for police to pull over a vehicle for the sole reason of being run through a license plate reader and registering a hit.