For years, the trusty seat belt provided the sole form of passive restraint in our cars. There were debates about their safety, especially relating to children, but over time, much of the country adopted mandatory seat-belt laws. Statistics have shown that the use of seat belts has saved thousands of lives that might have been lost in collisions.

Air bags have been under development for many years. The attraction of a soft pillow to land against in a crash must be very strong -- the first patent on an inflatable crash-landing device for airplanes was filed during World War II! In the 1980s, the first commercial air bags appeared in automobiles.

Since model year 1998, all new cars have been required to have air bags on both driver and passenger sides. (Light trucks came under the rule in 1999.) To date, statistics show that air bags reduce the risk of dying in a direct frontal crash by about 30 percent. Newer than steering-wheel-mounted or dashboard-mounted bags, but not so widely used, are seat-mounted and door-mounted side air bags. Some experts say that within the next few years, our cars will go from having dual air bags to having six or even eight air bags! Having evoked some of the same controversy that surrounded seat-belt use in its early years, air bags are the subject of serious government and industry research and tests.

In this edition of HowStuffWorks, you'll learn about the science behind the air bag, how the device works, what its problems are and where the technology goes from here.