SPRINGDALE Police in this Cincinnati suburb have turned to a mechanical watchdog that scans license plates on passing cars to try to snare fugitives, a practice that has drawn the attention of those who say it's an infringement on a driver's right to privacy.

The Mobile Plate Hunter 900 - two cameras mounted atop a cruiser - can read up to 900 license plates an hour on vehicles driving at highway speeds.

Some plates are difficult for the $20,000 machine to read because of awkward angles and other reasons, but it charts an estimated 85 to 90 percent of the plates that pass its radar.

The numbers are matched with a computerized list from the National Crime Information Center.

"It's unreal," Springdale Police Chief Mike Laage said. "It's the best technology out there."

The Ohio Highway Patrol has been using the plate hunter in six spots along the Ohio Turnpike, but Springdale police are the first to use it on regular patrols.

Since the patrol began using the scanners in 2004, it has recovered 95 stolen cars - valued at $740,000 - and made 111 arrests, said patrol spokesman Lt. Shawn Davis. The plate hunter has made roads safer, he said.

The scanner's gaze is too wide and it's an infringement against the innocent drivers whose plates get captured, said Jeff Gamso, legal director of the American Civil Liberties Union of Ohio.

Using the plate hunter to scan all license plates is a civil-rights violation and could lead to government abuse of the information, Gamso said.

"I think they should just knock it off," Gamso said. "Is the marginal benefit likely outweighing the danger of increased surveillance of everything we do?"