“License-plate readers are mass surveillance technology,” said Dave Maass, director of investigations at the Electronic Frontier Foundation, which advocates for better privacy protections. “They are collecting data on everyone regardless of whether there is a connection to a crime,” said Mr. Maass, “and they are storing that data for long periods of time.”

License-plate readers are part of police departments’ expanding arsenal of surveillance tools that also include social-media monitoring, facial-recognition software, internet-connected doorbells and camera networks—all of which have privacy implications.

Source: License-Plate Scans Aid Crime-Solving but Spur Little Privacy Debate – WSJ

Our smart phones are surveillance devices that we pay for our selves! Not only does Google monitor our location, all the time, even if location services is turned off, but numerous apps – even those having nothing to do with location services – also collect our location. It would be common for the average smart phone user to have multiple apps collecting their location data.