This isn't going to be what you want to hear, but after working in the automotive safety group of my company for 19 years, I really don't think there's much use for these rescue tools. A first responder--fireman or police officer--might need to break some glass or something, but I never heard of an individual who needed to cut away a locked belt or break glass to escape a wrecked car. Sure, there are people that need the "jaws of life," but you can't carry that in your pocket. You should also see how windshield makers try to make their glass impenatrable...it's not like you cause a pin point dent and the thing breaks apart. (Although, the side glass isn't as tough--make a note of that.)
And if I *still* thought I might need some kind of escape tool to save my life, I sure wouldn't:
a. Do it myself to make something out of a several layers of a credit card and a piece of spark plug, or
b. Leave it on a key ring, that could get locked in place during the crash when the steering column got all jammed up. What if you can't remove your key? Are you going to remove the emergency tool from the ring? If you're in a life-or-death situation, don't count on your fine motor skills!
DIY stuff can be cute...but--If you really think you need an escape tool to save your life, this ain't the one you want.
