As for the knife, I would recomend a spyderco Rescue. They are cheap and cut seatbelts very easily. If that knife alarms passengers and cops, then maybe a benchmade rescue hook might answer your question. I would also second or third the recommendaton of a spring loaded punch to break out windows. They arent as big as a hammer, or a s dangerous if you hit a passenger, and will bust out windows in a heartbeat.

Always remember one thing about knifes and seatbelts. Put yourself in a crash situaton and think about your state of mind. If you are in a bad enough wreck to be lcked in your seatbelt, you will probably be a little disoriented. You dont want to be thrashing all over the place with a razor sharp serrated knife in your hand, so keep that in mind when you think about size, etc. I know that some knives are designed with sheepfoot points (the rescue is one) and some even have dull points from the tip back about 3/4 of an inch to prevent you cutting someone else while you cut them out of the car.

I hope I answered your question.

Garrett