I have a spring loaded centerpunch attached to the drivers sunvisor in our P/U, but a strike with any sharp object will shatter a tempered window. In an emergency one could remove the key from the ignition, hold it with the tip pointing out from between two fingers, the blunt end of the key in your palm with a fist made, and punch the window hard. That might hurt a little bit, but should shatter the window. Or if a knife is handy, put the tip against he glass and whack the butt of the knife with your palm, same result...