It is smart to have a window-breaking tool in modern cars, but one should try to keep it in a place where they know it will remain during a car crash or rollover.
Theory is placing it in the unused cup holder but that might not be reality when needed.
Tie it to the inside mirror with a piece of thread. Up out of the way and so it doesn’t swing around. Like on the backside tied on one end of the tool and then wrap the thread around the mirror mount and then the other end of the tool so it hangs parallel to the mirror on the back side.