tssbulletproof.com

E1PmP TIL bulletproof glass can be manufactured to be bulletproof one way, but allow you to shoot through it the other way.
noVG TIL there is such a thing as one-way bulletproof glass. This allows you to return fire through the glass while still keeping you protected from the attacker (your shot leaves a bullet-sized hole, but doesn’t compromise the rest of the shield).