My understanding is that in Las Vegas, companies provide the licence plate readers to the police free of charge. These readers identify stolen cars, registered owners with outstanding warrants, expired tags, etc. in near real time to the patrol officer. In return the companies get to keep all the data from the scanners to do as they please.
The good part of this for me is that my daughter's Acura that was stolen twice was located both times within a couple of days and she got it back unmolested. The bad is that if you are driving a car that the registered co-owner didn't show for jury duty you will be pulled over on a pretext and grilled.