Despite the accessibility of bullet resistant windows for cars, it’s lengthy implementation, extreme cost and required expertise to install makes it an unideal option for both OPS and casual driving. The exception is for professional, non-impromptu use; vehicles specifically for security details and location constant OPS.
As for everyday casual use or relatively on the fly protection, window security film is the best option. It’s economical, reversible (removable) and can be easily applied by anyone to any vehicle.
This type of window shielding is similar to window tints. But instead of protecting against sun rays, it provides impact protection from blunt forces.
Window security film is widely available and is a common extended loadout or “shopping” item for operatives in the field. To be used on whichever vehicle is on hand if the situation potentially requires it.
It will do nothing against bullets of any caliber but is effective for many other attacks to varying degrees; punching, kicking, blunt instruments, hand thrown projectiles, small yield shrapnel etc.
While it lacks bullet resistance efficacy, it certainly augments the already present safety features of tempered glass found in all modern automobiles.