Providence Patrolman Miguel Mena-Torres glances at the computer screen connected to a camera mounted on the trunk of his cruiser that photographs license plates of parked or passing cars.

The Providence Journal / Steve Szydlowski

PROVIDENCE — Patrolman Miguel Mena-Torres was at Portland and Broad streets in South Providence when a tinny siren sound emanated from the laptop computer attached to the dashboard of his police cruiser.

He knew right away that a car that had just passed him was the subject of a BOLO — police lingo for “be on the lookout.”

Mena-Torres swung in behind a 2008 red Hyundai, put on the overhead emergency lights, and stopped the car, which had been reported stolen in East Providence. The female driver was arrested and charged.

The Providence Police Department’s newest high-tech acquisition — the Mobile Plate Hunter-900 — had just scored a “hit.” The Plate Hunter is an automatic license plate reader, which uses cameras with wide-angle lenses and optical character recognition software.

“As I turned, it caught the vehicle,” the patrolman remembered.

After a six-month tryout, police commanders are satisfied that the license plate reader is useful, although there have been no spectacular catches and the Mena-Torres stop apparently is the only time the technology has led to the recovery of a stolen car.

“What we’re determining right now is how best to use the technology,” said Maj. Stephen M. Melaragno, police director of administration. “We see the potential value …”

The department already owns one reader and is considering how many more units to get and what federal assistance can be sought to pay the approximately $20,000-per-unit cost.

“We’re trying to bring technology to the department that’s good for the working officer,” Police Chief Dean M. Esserman has said.

“…We are giving a police officer extra eyes. We’re giving them cameras that can pick up license plates when they drive by, faster than the human eye, and can alert their computer screen if it’s a stolen car, or if it’s a missing child, or if it’s someone with a warrant for their arrest.”

Rather than have the units in marked cruisers, which are generally confined to a patrol area, the Providence police are intrigued by the experience in New York City, where they are used in unmarked detective cars that range widely. The reader incorporates a GPS function, so suspect vehicles can be tied to a particular place at a particular time. That would enable the police, for example, to identify a burglar whose vehicle was parked near a break-in.

“It’s another tool on the investigator’s belt,” said Melaragno.

The visible parts of the Plate Hunter are two cameras clipped to the trunk lid, one to spot passing vehicles and the other, parked vehicles. It is a digital infrared system that can see day or night, rain or shine, capture still images and continuous video regardless of what state issued the plate, and remember what it sees in a data-storage receptacle tucked away in the trunk.

The Plate Hunter software instantaneously compares each plate with the huge lists of registration numbers associated with crimes and noncriminal violations in law enforcement databases, including the department’s own “hot sheet” of stolen cars and plates.

It can capture up to 3,600 plates per minute, manufacturer ELSAG North America boasts, but a cruiser never would move fast enough to come anywhere near that number.

The technology is an advanced version of that used by PayLock, the city contractor whose vehicles roam the streets, checking plates and looking to catch and boot the vehicles of parking ticket scofflaws.

With other vendors in the field, the police are undecided where to buy and are testing a product from Federal Signal on a second cruiser. And debugging has been necessary with both. The unit used by Mena-Torres for a while was reading vertical slats in metal fences as if each represented the number 1 on a plate. And the other unit mistakes the number 5 for the letter S.

While Providence’s use is the first in Rhode Island, more than 600 government agencies nationwide have bought Plate Hunters, with the closest known police departments being Brockton and Boston.

gsmith@projo.com