That's a great tool that I've used 100s of times. A 10 year old could effectively use it. A gentle push against the glass and it pops.
Without the proper tools, on non safety glass, the key is PSI. Large object impact areas are worse. Sometimes a hammer won't do it. If a hammer is what you have use the smallest head or the claw.
If a nearby car has a metal antenna (fewer and fewer these days), snap it off and hold it flat, lengthwise, against the window with the tip in a low corner of the glass Support hand holds it flat about a foot from tip and strong hand pulls it back. Let it go and it whips down and shatters the glass.
Hammers aren't automatic openers - http://youtu.be/wbOF11mQTjs
Sent from my iPad using Tapatalk