Am I missing something here; how exactly do you take care of an attacker from inside the car when your knife is on the key ring in your ignition especially with a seatbelt on?
If a carjacker is reaching in and grabbing you, what is his intent? He wants you out of his way so he can steal your car. Undo your seatbelt, say you'll do anything, say you're getting out of his way, say here's the keys (even though he does not want them removed from the ignition, you're just too afraid to think straight from his point of view). After you remove the key from the ignition, open the knife one handed below his line of sight. As he pulls you out, slash his inside forearm with your knife (and maybe the other forearm as well, depending...). That hand is now completely useless, and he is likely shocked that his plan suddenly went so bad. Maybe you can drive away then, or, if not, you can likely draw your gun at that point. He has only one working hand. Not as much a threat as when he started out.
Another approach to that scenario that does not involve a weapon is, if there are no innocent people in your path and your car is still running, floor it. The carjacker can let go or be dragged.
But there is a huge problem with this scenario. You should have been aware of your surroundings, found the guy suspicious, and took evasive action before he got close to you. You're just fixing your screw-up at this point.
Whenever I read about crime, which is, like, all the time these days, I imagine what I would do under the reported circumstances. I used to carry a regular pocket knife, but when I ran this scenario through my head, I realized I would need to be able to open a knife one handed, so I bought a tactical speedsafe knife. I also thought about variations to the scenario - what if x was different, what would I do then?
I'll add I've learned a great deal from The Best Defense Scenarios though I don't think they had this scenario. They show common, everyday situations, like walking to your car in a parking lot in low light, first with a typical reaction from a typical person. Then they comment on it and run it again with a better reaction, and finally a third time with a still better handling of the situation. There are three Michaels who create these scenarios, oddly enough. Michael Janich is the knife expert, and has written an excellent book on the subject. He talks about not worrying about bleed-out areas - instead you want to instantly disable the assailant and that involves cutting key nerves. Really excellent stuff. In the Best Defense Scenarios, a gun is usually involved in the solution to the problem. Their single most important point is to be aware of your surroundings and take evasive action. Don't let the assailant get near you.
[video]http://www.downrange.tv/blog/down-range-videos/the-best-defense-scenarios/[/video]
I would really like it if lots of posters would view these videos and/or other armed self defense stuff, and we could discuss it here. My purpose for having a gun is self-defense against armed attackers. I learn all I can from all credible sources I can get my hands on. I was hoping to find more discussion of armed self defense here on this site. But mostly the talk here is about technical aspects of guns. Not so much my cup of tea. Oh well, just suggesting....