JOHNSTON — After the snow hit, someone grabbed a Sawzall and slithered underneath the gleaming new Sportages parked at Metro Kia.

The thief zeroed in on each SUV’s antismog device, also known as a catalytic converter, an increasingly valuable commodity in the black market for stolen auto parts.

Platinum and other precious metals coat the composite materials inside catalytic converters, which make gases such as carbon monoxide and nitrogen oxide less harmful. The devices are a required exhaust-system component for the majority of SUVs, trucks and automobiles on the road.

With metal prices spiking this winter, some scrap yards will buy a converter for as much as $150. And victims can pay as much as $1,000 in parts and labor to replace the device.

Catalytic converter thefts, once unheard of, are happening with regularity across Rhode Island, and the nation.

For example, Sao Pongvongkeo, returned to his Johnston home Tuesday afternoon to find fluid leaking from the undercarriage of his automobile, according to a police report. A criminal had used bolt cutters to remove the device.

Earlier that day, another man, Ronald M. Ash, of Smithfield, discovered that someone had taken a converter off his Toyota pickup while it was parked at the corner of a lot at 228 Putnam Ave. in Johnston, according to the police.

In all, 10 new vehicles were hit at Kia Metro on Hartford Avenue in Johnston sometime between Dec. 13 and Dec. 29, according to Johnston Deputy Police Chief Gary W. Maddocks Jr. A detective found a saw blade underneath one of the cars.

The Sportages had been moved to the corner of the auto lot to accommodate snowplowing. They didn’t start when it was time to move them back.

Cranston authorities reported a string of converter larcenies late last year and East Greenwich saw some thefts in December, according to Johnston Detective Joseph Arcuri Jr.

The police say converter thieves tend to target trucks and vehicles with higher ground clearances. That makes it easier for a thief to slip under the vehicle and saw off the converter.

The precious metal coatings in the converters — platinum, rhodium, and palladium — have dramatically increased in value over the past year.

An ounce of platinum costs more than $1,500, up more than $400 from last year’s prices, according to published reports. That much rhodium is worth $7,000, up more than $6,500 since 2004.

Jeffrey Frank, manager of a Midas garage in Providence, said one customer’s truck was hit while parked outside at the Home Depot in Providence a few months ago.

The cost of replacing the converter can range between $300 and $800, depending on the year and make of the vehicle, Frank said.

William Santa Maria, a mechanic at Neighborhood Auto Center in Providence, said he’s replaced three conversion systems within the past 50 days.

“One customer said he was in the supermarket and when he came out it was stolen,” Santa Maria said.

By yesterday afternoon, Jamie Sousa, the owner of a garage in Pawtucket, was planning out the mechanics of replacing several converters on a mid-90s Ford Explorer.

This would be his third converter replacement since the middle of last year. Before that, he’d never met a customer who needed to replace stolen converters.

He said he will start working on the Ford Explorer today. The job will take four to six hours. It will cost $650.

“It will take me a good part of the day to fix it,” he said. “It’s basically the whole exhaust system because of the damage they did.”

mreynold@projo.com