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Mercedes-Benz ML350.

The GPS-based cell phone technology that appears to have helped track down the alleged Boston Marathon bombers is pretty common.

Besides luxury brands like Mercedes-Benz and BMW, which have their own telematics systems, millions of General Motors vehicles are equipped with the best-known system, GM's OnStar.

OnStar relies on what basically amounts to a cell phone receiver/transmitter installed in your car. It has been standard equipment on most GM products across all its brands, like Buick, Cadillac, Chevrolet and GMC, since 2002. OnStar is also available for other cars, as an aftermarket accessory. The down side is, customers have to pay to maintain a subscription.

One of its biggest selling points is that OnStar automatically provides emergency notification if an air bag goes off in your car. It also provides emergency services with your car's precise location. That also means if your car is stolen, the same hardware in your car can tell the police where it's located. Some other mass-market brands also have their equivalent, like the Toyota Safety Connect system.

GPS technology came into play in the recent manhunt for the alleged Boston Marathon bombers, after the suspects allegedly car-jacked a Mercedes-Benz M-Class sport-utility, a 2013 ML350, before midnight on April 18.

Police said the owner fled when the men stopped to buy gas. According to a story in the Boston Globe, the victim told police he left his cell phone in the car, which could be tracked, and he also told police that his car could also be tracked using the Mercedes-Benz GPS system. The company calls it "mbrace2," for the second generation of the mbrace system. Before that, the prior generation was called Tele-Aid.

Mercedes-Benz USA LLC confirmed separately that police contacted the company during the manhunt for the bombers and asked Mercedes-Benz to use the mbrace system's "Stolen Vehicle Location Assistance" function to help find the vehicle.

Later that night, police said Tamerlan Tsarnaev was killed in a shootout in the early morning of April 19, and his younger brother Dzhokhar Tsarnaev was arrested that evening in Watertown, Mass. Police said he is charged with "use of a weapon of mass destruction" and "malicious destruction of property resulting in death," from the April 15 Boston Marathon attack.

Early in the morning on April 20, Mercedes-Benz USA CEO Steve Cannon tweeted, "Just found out that our mbrace2 technology in the stolen Mercedes helped locate the Boston terrorists! Thanks to our amazing law enforcement." Mercedes-Benz wouldn't disclose precisely what was done.

In OnStar's case, the way it works is that OnStar sends a command for the OnStar unit in the vehicle to emit an electronic signal, or "ping." It's undetectable to the occupants, but the "ping" shows up on the GPS-cell phone network, and discloses the vehicle's precise location to OnStar. To track a moving vehicle OnStar has to keep pinging; it's not continuous.

OnStar handles an average of about 320 calls per month from law enforcement to locate stolen vehicles, according to spokeswoman Cheryl McCarron. She said the owner's OnStar subscription has to be active. An inactive account can't be re-activated without someone in the vehicle pushing a button, McCarron said.

Nearly all the time, the vehicle in question is sitting still, she said. In around three to five cases per month, she said OnStar is called upon to intervene with a moving stolen vehicle. Typically in these circumstances there is a police vehicle in direct contact with OnStar watching the stolen vehicle in question, McCarron said.

OnStar can force a moving vehicle to slow down to idle by electronically disconnecting the accelerator. OnStar can also prevent a vehicle from being restarted once it's been turned off. OnStar has been used successfully to foil car-jackers, the company said.

The Mercedes-Benz mbrace system doesn't have those features, but the Mercedes-Benz SUV was still a bad choice for someone who wanted to disappear.

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