a) The added protection is not installed afterwards, but is already integrated into the bodyshell during the vehicle assembly. So, it's different from getting your current four-wheeler bulletproof.
b) The S-Guard is protected by high-alloy special steels and bulletproof glass. When designing this armoring, the Sindelfingen specialists cover virtually the entire sedan: during assembly, protective elements are installed in the doors, rear wall, sides, roof lining, bulkhead, and other sections. Yeah! In case you already are worried about door gaps, they are designed in a way that an impacting bullet is diverted into a kind of labyrinth, so that it cannot penetrate the seam. Sit and play God!
d) To give you company on-board there's a fire extinguishing system with twelve jets.
e) Just in case, if a mere immortal doesn't satiate you and you'd like to play James Bond the car has a special protection fuel tank that can seal itself if hit by bullets. So, no blow-up jobs.
f) Bad news is you can't use "flat tire" excuse next time you are late with S-Guard. Michelin has developed a special run-flat tire with an inner thrust ring on a special rim. This ensured good emergency running characteristics, even after a complete loss of pressure.
So, own one and live long.