The inside of a specially equipped police cruiser sounded a lot like a grocery store checkout.

But the constant beeping was actually checking license plates.

The instantaneous rate — easily 20 vehicles per minute during a ride-along with veteran Officer John Ritchie — would have made a grocery cashier cringe.

The software, which was recently purchased by police here, checks for wanted persons, unregistered vehicles, revoked registrations and stolen cars and can be used for investigative purposes, Officer Ritchie said. Police can check the plates of moving or parked vehicles.

Rather than one officer running radar and attempting to key in license plates — perhaps at a rate of 100 per shift — the system can run hundreds of plates in a couple of minutes, enhancing the officers' time on motor vehicle enforcement.

The Southbridge Police Department recently purchased ELSAG North America's license plate recognition program, which is used more heavily in New York, Maryland, Washington, D.C., Virginia, Connecticut and Ohio.

About 20 departments in Massachusetts use it. ELSAG spokesman Nate Maroney declined to identify the others because of nondisclosure agreements.

The program costs about $20,000, including hardware, software and four years of support, Mr. Maroney said.

Infrared cameras are placed on the cruiser's exterior, and a network and power junction box go inside, along with a laptop computer for the officer to read and enter data.

ELSAG, which is based in Brewster, N.Y., and has a manufacturing facility in Greensboro, N.C., says the recognition software can capture 3,600 reads per minute on a high-speed road.

Officer Ritchie said Somerville's department was one of the first in the state to use the program, and soon after it helped the urban community find about five stolen vehicles a day.

Officer Ritchie said he usually kept an eye out for hanging license plates, or became suspicious if the car was dirty and the plate was clean, or vice versa.

An advantage to the program is it takes out profiling, Mr. Maroney said.

“It's just looking at the license plate, reading it and reporting back,” he said. “So everyone is treated fairly.”

The technology's origins were for mail sorting.

“It was using optical-character recognition to look at ZIP codes and point it in the right direction for mailing,” Mr. Maroney said. “Where else do you see the configuration of numbers and letters? License plates were a natural extension of that. The technology got retooled to be able to do this.”

The program is about six years old.

ELSAG is a subsidiary of Finmeccanica, a big Italian defense company. Six years ago the system was a joint venture between Finmeccanica and Remington Arms, the manufacturer.

Finmeccanica was trying to get a foothold in the United States and capitalized on the Remington brand to drive the product into the market. Within two years of starting the relationship, the product got up and running and Finmeccanica bought out Remington, Mr. Maroney said.

The company would like for the technology to be as commonly used with police as a radar detector or Breathalyzer, he said.

Chief Daniel R. Charette said his department paid for the program with money left over from last year's budget. He said he took the town manager to an event for Massachusetts police chiefs that vendors attended.

With budget cuts, it's become increasingly difficult to keep personnel, which accounts for up to 90 percent of most department costs, he said.

“There's very little you can cut before you start losing people. We've had to try to find ways to do more with less, and one of those ways to do that is with technology,” the chief said.

During his traffic enforcement assignment, Officer Ritchie said that the state provides a list of information about stolen vehicles. There were no hits during a ride through downtown and two grocery store plazas.

There were also no unregistered or uninsured licenses.

The officer explained the lull.

“People have gotten a lot better in keeping their cars registered and insured because of the fines and the effects of all the surcharges,” the officer said.

State data seem to affirm the claim. In 2009, police wrote 45,696 tickets for unregistered vehicles. In the first three quarters of 2010 they wrote 29,255 such tickets, a Registry of Motor Vehicles spokesman said last week.

The recognition system doesn't only read licenses. During the ride-along it read the lunch special of a mom-and-pop restaurant and a sign at a collection site for donating clothes.

No citation was issued.

“It doesn't know,” Officer Ritchie said. “Anything that has printing and writing on it, it's going to read.”

Officer Ritchie said the department has only had the system in place a short time and can't say yet whether it has led to more arrests.

It's only utilized on certain shifts right now because of limited staffing.

Officer Ritchie said the software can even confirm or refute a suspect's alibi, because it records the location of the car and time it was there.

Meanwhile, the chief acknowledged that as technology gets better or is more available, the invasion-of-privacy question is important to ask.

“Personally I don't feel it's any kind of invasion, because we always fall back to the same thing with policing — driving a motor vehicle is not a right, it's a privilege. If you want to be on the road, you are required to register, you are required to follow certain criteria, and if you don't you can be held accountable for those actions.”

Officer Ritchie said he's been asked if the program has facial recognition.

“I don't think we have a need for that at this point,” he said. “But someday, who knows? This software might be tied in to facial recognition.”

He said he was also asked if the program could take a picture of a perpetrator as he drives by.

“Not unless he has a license plate under his chin,” he said.