The OnStar safety system is escaping from the boundaries of General Motors and will be available in the spring to people who own cars and trucks made by other auto companies.

To get the service, though, people have to buy a special OnStar rearview mirror for $299 and then pay a monthly fee that starts at $18.95.

The system, known for its television commercials with operators sending help to people in car crashes, will be sold at Best Buy and other retailers for use in non-GM vehicles and older GM cars and trucks that don’t have the service, the company said Tuesday night at the Consumer Electronics Show in Las Vegas.

GM says the mirror will work on 99 percent of the 20 top-selling non-GM vehicles from the past 10 years, or about 55 million cars and trucks.

OnStar, which began in 1996, has more than six million subscribers in the U.S., Canada and China.