BANGOR, Maine — Thieves have long targeted car stereos, air bags, high-intensity headlights, even pocket change from the ashtrays. But now they are slithering under vehicles and cutting away the catalytic converters.

The anti-pollution devices contain small amounts of platinum, rhodium and palladium, and the value of these precious metals has been rising sharply, making catalytic converters a hot commodity in more ways than one at scrap yards from Maine to California.

"These thieves catch on quicker than us honest people," said Kennie Andersen from Andersen Sales and Salvage Inc. in Greeley, Colo.

In Bangor earlier this month, thieves brazenly removed catalytic converters in a busy hospital parking lot in daylight. Police also have fielded reports of thefts in recent weeks in Alabama, California, Louisiana, New York, North Carolina, Ohio and Tennessee.

Old catalytic converters are usually sold for scrap. The prices paid by scrap yards for one of the devices have generally risen from $5 to $30 a decade ago to $5 to $100 nowadays. Some models can fetch up to $150.

Frank Scafidi, National Insurance Crime Bureau spokesman in Sacramento, Calif., had no immediate figures on catalytic-converter thefts. "We have regular reports of these things being stolen, but it's sporadic. It's not the kind of thing that's an epidemic," he said.

Stealing one of the devices often requires little more than a battery-powered metal saw to cut through the exhaust pipe, and it takes only minutes. Once the catalytic converter is gone, the car may look fine, but the exhaust lets out a NASCAR-like roar when the driver turns the key.

While some unscrupulous scrap dealers ask no questions, the Institute of Scrap Recycling Industries issues e-mail alerts whenever thefts of converters are reported and urges members to screen suppliers and photocopy the driver's licenses of those who sell them, said Bryan McGannon, spokesman for the trade group.

"Playing by the rules is good business," he said. "Nobody wants to be tied up in a police investigation where your materials are tied up for weeks."

In Bangor, medical secretary Karen Thompson was summoned by hospital security to the parking lot, where someone had cut away the converters from a couple of vehicles, including her 2006 Toyota Tundra pickup. When she started up the truck, it rumbled as if there were no muffler.

"It was really, really loud. The rearview mirror shook," Thompson recalled. The cost of replacement and repairs at her Toyota dealership was $2,100.

Millions of catalytic converters have been put on cars and trucks since they were introduced in 1974. Inside most of them is a ceramic honeycomb coated in a material that contains platinum, rhodium and palladium, which serve as a catalyst to reduce tailpipe emissions of unburned hydrocarbons, carbon monoxide and nitrogen oxides.