Best Defense TV had a video from police training where they took a vehicle's radio antenna, bent it over 90 degrees, unscrewed it and busted out a side window with very little effort, hitting in the corner of the window. Much less effort than you were putting into it with the knife. They also tested one of the 50 cent keychain breakers, worked like a champ when used in the corner of the window. Unfortunately, I can't find anything of the sort on youtube.