I have previously had to install simple things like doorbells for deaf people, which is done through a very strobe light that can be seen from almost the entire apartment... if you're not behind a closed door at least.

The idea of it being genuinely difficult for a person to be warned or notified is terrifying. Put your phone in your bag and you might as well have left it at home. Honking, people yelling or screaming for you to move out of harms way, even air sirens... You'll have no idea.