When thieves repeatedly struck her Mount Airy street last summer, Sara Steele tried to protect her Toyota Prius.

Burglars had stolen her neighbors’ catalytic converters, an auto part made with metals worth more than gold. Not wanting to be the next victim, she ordered a steel shield to bolt to the bottom of her car and guard the expensive device.

She was too late. Before the shield arrived in August, Steele started her normally quiet hybrid and it roared like a motorcycle. Someone had sawed off her catalytic converter, an emissions-control device between the engine and muffler.

“It was parked right in front of my house,” Steele said. “If they had broken into it, the alarm would have gone off. I didn’t hear a thing.”

Catalytic converter thefts are on the rise nationwide, fueled by record prices for the precious metals in the auto part, which helps gas-powered engines burn cleaner. Demand for the metals, palladium and rhodium, has climbed in recent years as governments pass stricter emissions laws to cut pollution. The auto industry is the metals’ biggest consumer.

Just five years ago, an ounce of palladium was worth nearly $600, according to Johnson Matthey, a British chemical and technology company. Now it costs about $2,900. In comparison, an ounce of gold is worth nearly $1,900. Rhodium is even more valuable, with prices above $28,000 an ounce this month.

Those spikes are driving an underground market for items that contain palladium and rhodium. A single catalytic converter contains just a few grams of the precious metals, but burglars can sell the stolen parts at scrap yards for hundreds of dollars, law enforcement officials said.

“It’s quick and easy money, and the transactions are difficult to trace,” said Jan McDermott, supervisor of the auto theft unit at the Philadelphia District Attorney’s Office.

In Philadelphia, there were 489 auto theft episodes in 2019 in which the word catalytic or converter was mentioned in investigative notes, police say. There were 866 in 2020, a 77% increase. The thefts are on pace to jump again this year, with 586 reported episodes as of May 7.

Other cities, such as St. Louis and Seattle, have reported a rise in the thefts. Denver saw a 1,600% spike in stolen catalytic converters during the pandemic.

The crimes take just minutes. Someone can quickly jack up a car and use a battery-powered saw to cut out the device from underneath.

“We’ve had it at some of our local shopping centers, where literally people are in there for minutes, and during that time frame, it happens to them,” said Cherry Hill Police Lt. John Moyer, who heads the Police Department’s investigative division.

Cherry Hill officials know firsthand. About 2 a.m. on a Monday this month, thieves stole 10 catalytic converters in 40 minutes from municipal vehicles parked outside the Public Works Department’s maintenance building, Moyer said. An investigation is ongoing.

Elevated trucks are easy targets because a jack is not required. But thieves appear to prefer the Toyota Prius, which uses more grams of the precious metals, according to law enforcement officials and mechanics. A Toyota spokesperson called the thefts “an industry-wide challenge” and said “the Prius is just as much at risk as any other vehicle.”

“There are groups that travel around the country, and they’ll come into town and they’re looking for Toyota Priuses and nothing else because those are the highest-valued ones,” said Joseph Boche, chair of the subcommittee on catalytic converter thefts for the International Association of Auto Theft Investigators (IAATI). Mitsubishi’s Outlander and Honda’s Element and CRV models are favorite targets, too, Boche said.

The thefts can cost consumers upward of $3,000 in repairs, depending on the vehicle and their insurance coverage. Derek Warnick, of Chestnut Hill, paid about $800 after his Prius’ catalytic converter was stolen in October. He caught the thieves in the act about 5 one morning and ran downstairs as they fled. His car appeared unscathed — until he tried to drive it.

“I went to back up and there was just this loud, horrendous sound,” he said.

Mechanics making the repairs blame whoever is buying the obviously stolen parts. T.J. Frearson, owner of the Carpenter Lane Garage in Mount Airy, noted that mechanics unbolt catalytic converters to replace them. They don’t hack them out.

“You can clearly tell that they’ve been just cut off the car,” said Frearson, who has had about 10 customers with missing catalytic converters over the last year.

Mechanics have also seen Prius owners request installations of “cat shields” — steel plates that cover catalytic converters and cost about $200, like the one Steele ordered too late.

Boche, of the IAATI, suggested that owners engrave their license plate or vehicle identification numbers on the devices. That way, police can at least trace a stolen part back to its owner.

Boche has called for laws to regulate scrap sales, requiring owners to identify themselves, prove they own the catalytic converters, and limit the use of cash in such sales. He said police need to be able to access those transaction records.

Although emissions rules have driven the demand for rhodium and palladium, the pandemic likely also impacted prices. About 80% of the world’s rhodium comes from South Africa, where coronavirus shutdown orders and unrelated processing plant outages slowed production.

“In the rhodium market, if something happens to impact South African mining, then it does definitely have a far larger impact on supply and demand dynamics,” said Wilma Swarts, director of platinum group metals at the London-based research consulting firm Metals Focus.

The global domino effect from those market forces may have reached Bill England’s home last month. Someone stole a catalytic converter from England’s Prius while it was parked in his driveway in Elkins Park.

“I would have thought it was safe,” he said. “I have two lights on the driveway, just as a deterrent.”