DETROIT — Say some clown steals your car from the parking deck at work.

If it's equipped with General Motors' OnStar service, he could be in for a big surprise and you could get a little revenge — and even see your car again.

Starting with about 20 models for 2009, the service will be able to slowly halt a car that is reported stolen, and the radio may even speak up and tell the thief to pull over because police are watching.

OnStar already finds 700 to 800 cars per month using the Global Positioning System. With the new technology, which OnStar President Chet Huber said GM will apply to the rest of its lineup in future years, OnStar would call police and tell them a stolen car's whereabouts.

Then, if officers see the car in motion and judge it can be stopped safely, they can tell OnStar operators, who will send the car a signal via cell phone to slow it to a halt.

"This technology will basically remove the control of the horsepower from the thief," Huber said. "Everything else in the vehicle works. The steering works. The brakes work."

GM is still exploring the possibility of having the car give a recorded verbal warning before it stops moving. A voice would tell the driver through the radio speakers that police will stop the car, Huber said, and the car's emergency flashers would go on.

"If the thief does nothing else it will coast to a stop. But they can drive off to the side of the road," Huber said.

With the current version of OnStar, drivers can call operators for emergency help, and OnStar operators will contact a car if its sensors detect a crash. The service has about 5 million subscribers.

Those who want OnStar but don't like police having the ability to slow down their car can opt out of the service, Huber said. But he said their research shows that 95 percent of subscribers would like that feature.

OnStar, including the first year's subscription fee, is standard on most of GM's 2008 vehicles. After the first year, the subscription price is $16.95 a month or $199 annually for basic service, which is to include the stolen-vehicle slowdown feature when it's available.

GM would be willing to sell the technology to other automakers in an effort to cut police chases, Huber said.

The new technology likely gives OnStar and GM a leg-up on competitors that market vehicle tracking devices aimed at retrieving stolen vehicles, said Jack Nerad, executive market analyst for Kelley Blue Book in Irvine, Calif. He predicted being able to stop a stolen car would appeal to consumers.

"Once they hear it can be done, I think it will get considerable play," he said.

LoJack Corp., of Westwood, Mass., produces vehicle tracking devices that help authorities locate stolen vehicles but not communicate with them. And SPAL USA in Ankeny, Iowa, sells an anti-car-jacking system with a personal identification transmitter that prevents thieves from using the vehicle.

If it spreads, the technology could make dangerous police chases a thing of the past. Last year, 404 people were killed nationwide in crashes involving police pursuits, according to the National Highway Traffic Safety Administration.

In California, for example, there were 7,633 police pursuits in 2006, leading to 27 deaths and 771 injuries, according to data from the California Highway Patrol. Those figures represented a decline from 2005, when California authorities were involved in 7,950 pursuits, which were linked to 32 deaths and 1,201 injuries.

Joe Farrow, deputy commissioner of the California Highway Patrol, said about 15 percent of the pursuits are at speeds of 90 mph and greater. The OnStar system could help chases end safely, he said.

Farrow said his agency has sought public-private partnerships that could improve technologies used in police pursuits. The OnStar system was intriguing, he said.

"There are some high-speed chases that we have out here that we'd like to bring to a halt," he said.

Farrow said CHP officers are trained on pursuits every three months and the agency has worked to improve its chase policies.

OnStar's technology could evolve and perhaps make a stolen car impossible to start, Huber said.

"This isn't the last announcement you'll hear from us in this category," he said.