Wealthy suburbanites, you may want to put your car keys away.

South Side thieves have targeted luxury cars in 40 wealthy towns across the Chicago area from Lake Forest to Barrington to Hinsdale, officials say.

The bandits slipped into unlocked cars and drove away using keys or fobs they found inside cup holders or consoles.

Authorities believe at least 70 vehicles — BMWs, Audis, Range Rovers and Infinitis — were pilfered by a loosely organized Chicago theft ring this year.

Most have been recovered in South Side neighborhoods. One owner couldn’t recognize his car because the thieves had tinted the windows.

Police have arrested about 15 suspects, most of them juvenile gang members. Detectives believe they were using the cars while committing armed robberies and shooting at rival gang members.

Video showed a black Audi that was stolen from Lake Forest hitting speeds of more than 125 mph on Interstate 94 while the passengers waved guns out of the window. A Lincoln stolen in Burr Ridge in July was later spotted at crime scenes in St. Charles, Lake Forest and Barrington before it was recovered in Chicago, police say.

The thefts started on a cold winter day on the South Side after gang members searched Google for mansions they could target, Chicago Police Lt. Ed Wodnicki said.

“They jumped in a car at 2 a.m. and drove to the northern suburbs,” he said. “They walked up driveways to these nice houses. They would try the car door and find keys in the cup holder. These cars were ready to be stolen.”

On Aug. 9, Wodnicki was conducting a sting involving a laptop computer stolen in the northern suburbs. A tracking device showed the computer was on the South Side.

Police set up a ruse, offering $500 for the recovery of the computer. Wodnicki dressed in civilian clothes and met a man who sought the reward.

Wodnicki arrested the man in a bank parking lot. Wodnicki found a loaded .40-caliber pistol and a high-capacity magazine in the car the man was driving.

The man confessed to the computer theft and then spilled the beans on the luxury car theft scheme, Wodnicki said. He’s expected to be charged in federal court with being an armed habitual offender.

On Aug. 12, the Chicago Police organized a task force with suburban police departments to investigate the thefts.

On the Thursday and Friday before Labor Day, officers drove throughout the South Side with license plate scanners and recovered 20 luxury cars that were stolen from the suburbs, Wodnicki said. Of the 70 cars stolen this year, about half a dozen haven’t been recovered yet, he said.

Oddly, the ring wasn’t selling the cars to chop shops for parts. Instead, they were using them in crimes and then dumping them, Wodnicki said.

After they would steal cars, “one of the other things these brain surgeons did was burglaries in liquor stores,” Wodnicki said.

He said the suspects were captured on surveillance cameras stealing booze, which allowed police to identify them in the car thefts.

Wodnicki wouldn’t confirm whether the ring stole a sports car that resulted in a police-involved shooting in Chicago this summer.

But he said: “It sure looks to us that any vehicle that you steal out of the rich suburbs and we find on the South Side are part of this pattern.”

On July 28, Chicago Police officers chased a 2002 Jaguar convertible that was stolen from Bolingbrook. An officer fatally shot Paul O’Neal, the 18-year-old driver, after a foot chase in the 7300 block of South Merrill in the South Shore neighborhood.

Moments earlier, officers had fired at the Jaguar, which crashed into a police vehicle. The three officers who fired their weapons have been placed on desk duty while the Independent Police Review Authority investigates.

Just before that incident, police had been chasing a stolen BMW in the same area.

Wodnicki said most of the thieves belong to one of four gang factions on the South Side. The purloined cars were recovered in four South Side police districts: Wentworth, Grand Crossing, South Chicago and Calumet, he said.