(NYTIMES) - Professor of economics Michael Kevane did not give a second thought to parking his 2005 Toyota Prius in his driveway one rainy evening last month.
But the next morning, when his son Elliot went to start up the car, it emitted a loud noise that woke up the neighbours.
The reason for the ruckus: A thief in the night had made off with the car's catalytic converter, a critical emissions-control device that contains trace amounts of precious metals more valuable than gold.
Two days later, his sister Jean also had the catalytic converter stolen from her 2003 Honda Accord LX.
Stricter car emissions rules around the world have sent demand for the precious metals in catalytic converters surging. That has pushed up the asking price for some of the precious metals used in the device - like palladium and rhodium - to record highs.
From about US$500 an ounce five years ago, the price of palladium quintupled to hit a record of US$2,875 an ounce last year, and is now hovering between US$2,000 and US$2,500 an ounce, above the price of gold.
Rhodium prices have skyrocketed more than 3,000 per cent from about US$640 an ounce five years ago to a record US$21,900 an ounce this year, approximately 12 times the price of gold.
The metals' prices, in turn, are fuelling a black market in stolen catalytic converters.
One can be sawn off from the belly of a car in minutes and fetch several hundred dollars at a scrapyard, which then sells it to recyclers who extract the metals.
Across the United States, the police are reporting a surge in cases.
Catalytic converters, the shiny bulbous contraptions found between a car's engine and the muffler, might seem like an unlikely target of a national crime wave.
Required in all petrol cars and lorries sold in the US since 1975, the converters have a honeycomb-like interior - coated with precious metals like palladium, rhodium and platinum - that scrubs the worst toxic pollutants from the car's exhaust.
The presence of those metals has always made catalytic converters a target, and incidents of theft - which can set owners back US$2,000 (S$2,650) in repairs - go back years.
But a global trend towards stricter tailpipe emissions rules, as well as more rigorous enforcement after the Volkswagen emissions scandal, in which the carmaker illicitly modified its vehicles' pollution controls to seem cleaner than they really were, has led to a surge in demand for higher-performance catalytic converters and the valuable metals that make them work.
Rhodium, in particular, is effective in reducing levels of nitrogen oxide from a petrol car's tailpipe emissions.
And "we've had a very steep step up" in nitrogen oxide rules around the world, said Ms Wilma Swarts, director of platinum group metals at the London-based precious metals research consultancy Metals Focus.
About 80 per cent of demand for palladium and rhodium now comes from the automotive sector.
At the same time, the effects of the pandemic on mining in South Africa, a major producer of rhodium, has kept supply limited.
For carmakers, the metals boom has jacked up the cost of producing petrol vehicles.
Mr Max Layton, a London-based commodity analyst at Citi, estimates that soaring metal prices added US$18 billion to the global auto industry's production costs in 2019, gobbling up 15 per cent of total cash flow, and that those costs surged further last year.
At current prices, he said, the industry as a whole was set to spend more than US$40 billion this year just on metals for catalytic converters.
The escalating costs, Mr Layton said, were "putting pressure on carmakers to shift to battery electric vehicles as quickly as possible".
Some owners of petrol vehicles are going to extremes to protect their vehicles.
After being hit with three converter thefts in quick succession last year, Mr Jerry Turriff, the proprietor of Jerry's Certified Service and Towing in Milwaukee, Wisconsin, has resorted to deflating the tyres of some of his customers' most at-risk vehicles to deter thieves from crawling underneath.
"It's unbelievable," he said. "Now if I have a vehicle I think is going to be targeted, I take the air out of the tyres, so (the thieves) can't slither underneath."
Mr J. C. Fontanive, a sculptor in Brooklyn, New York, bought a used 2008 Prius in the summer, spurred by concerns over taking public transportation amid the pandemic. Then last month, he drove it to a friend's place and "it sounds like Nascar", he said of the noise.
He did not have full car insurance coverage, so he had to pay US$3,200 out of pocket for a replacement and repairs - half the price he had paid for the car itself.
Determined to deter future thieves, Mr Fontanive, who often uses metal in his artworks, drew on his metalworking skills.
He bought an after-market metal guard for his catalytic converter, then made his own modifications, with security screws and hardened steel bell pins that would be hard to saw through.
"I really went overboard," he said. "If they look under my Prius now, they're just going to be like: 'No way'."