I'd be cautious about using keys or a knife blade. You'd have to hit keys awfully hard into the window - with a risk of hurting your hand as well. I'd be worried that a knife blade would tend to skate across the smooth surface of the window glass.

You need an impact tool:
* Center punch.
* Impact end of the AK-47 knife.
* A small hammer, where one end of the hammer anvil comes down to a cone (e.g. a small rock hammer).

Pete