Sandy Boyce, a 72-year-old retiree in Sedona, Arizona, first saw the cameras around town this summer. They were black and sleek, mounted on tall poles under large solar panels and positioned at intersections to snap images of cars as they drove by. Boyce had read that Sedona had quietly signed a new contract with Flock Safety, the country’s largest provider of automatic license plate readers (ALPRs), which had installed four cameras to build a database of every car that drove by. Eight more