If you want to use a folding knife to go through the window of your car ... get a hold of one of the AK-47 folding knives from Cold Steel. Seriously. Checkout their web site at www.coldsteel.com and take a careful look at the AK-47 under the folding knives section. Note in particular the reinforced back end of the knife (opposite end from the blade). That design is no accident - it will serve you well if you need to break glass or discourage someone from punching your face.

Pete