Mercedes-Benz will begin equipping its cars with inflatable seatbelts for rear passengers, making it the second automaker to use the safety technology.

Mercedes said the belt would be introduced on an upcoming luxury car. A likely candidate is the redesigned S-class sedan, which the German automaker is preparing to put into production next year. Prototypes have been spotted undergoing hot-weather testing. A reveal is likely early next year, possibly at the Detroit or Geneva auto shows.

Ford introduced inflatable rear belts on the redesigned 2011 Ford Explorer. It also offers the technology on the Ford Flex and the Lincoln MKT wagons, and charges about $200 for the option. Ford has said the redesigned Mondeo sedan for Europe will use the technology.

The technology marries a small airbag with the rear belts' shoulder strap. When the car senses a crash, the airbag in the belt inflates. The expanded bag increases the width of the belt, helping to spread crash forces over a wider area of the passenger's torso and reducing the chance of injuries.

Mercedes says it does not intend to use the inflatable belts for front seats. It notes that front passengers are protected by front, side and, in some cases, knee-bolster airbags.