SUGAR LAND, Texas -

While people are working out their bodies, crooks are working on damaging their cars.

Sugar Land police said thieves are stealing catalytic converters.

A woman parked her car at the LA Fitness near the Southwest Freeway and the Grand Parkway about 11:15 a.m. Saturday. When she came out an hour later, her car sounded strange because her catalytic converter had been stolen.

Police said it's a crime of opportunity.

"They see a vehicle they want and if you're not there, they have that opportunity to seize it," Officer Lauren Stockholm said.

Stockholm said there have been at least 10 similar cases around the city in the past month. Police are increasing patrols.

"We have officers on bikes, officers in unmarked vehicles," she said.

It takes about a minute to steal a catalytic converter.

Mary O'Garro-Greene drives a Toyota 4Runner, which is a popular target for the thieves.

"This is the first time I'm hearing about it," she said when KPRC Local 2 told her about the thefts.

Police said most of the thefts happen during the daylight hours.