Yesterday I spoke to a friend of mine who is a fire fighter. Het told me at work they don't use a resQme or something similair to brake windows, but they use a little pen from Holmatro to break the glass. He had a spare one so gave one to me
The tip of the pen is sharp and at the back has a counter weight, the spring in the middle makes it possible to pull back the counter wieght and on release it will break the glass. Only works on tempered glass (e.g. side windows)
Here in Europe Holmatro is a big name when it comes to resque tools.