Still, my children's car seats failed the test. Small people sit in back. The safest place in the car is the back seat, regardless of whether the passenger side of your front seat has an air bag. If it does, however, and you install your safety seat there anyway, you're playing Russian roulette with only one chamber empty. Never use a car seat before you read the instructions.
Car seats are frequently incompatible with the seat belt systems in cars.
The only way to know if the seat you've selected works with the car you drive is to read the manuals that come with each. This is no easy task, unfortunately, thanks to the Neanderthal literacy level of most technical writers, but do the best you can with the books. Then call the 1-800 number in each to clear up any confusion. If the auto manufacturer says you need to use a locking clip to secure the seat to the car, use one. If you don't, the seat is worthless in an impact.