As far as I know there have to be a few things to take place for the air bags to deploy! 1st the impact and 2nd a rapid deceleration! Most impact sensors are placed under the front headlights! So if the impact doesn't hit them, then the bags might not fire! Unless Chrysler have them all along the crush beam?. There use to be 2 types od seatbelt pre tensioners. One is a pyrotechnic (An explosive charge! Or bomb for a better word) that is encased in metal that sends a plunger down a hollow metal tube that is attached to a wire that pulls your seat belt back into the seat and you with it! The other is a mechanical system that does the same job, but notdas effective, hence why most manufacturers use the 1st one.

As for what chrysler adopted!? I'm not sure! But if they had gone off! It would have been an expensive repair job.