So initially I didn't care about zombies getting alerted by sound or anything really, this was just a tutorial, but as I started expanding the game and the interactions I noticed I wanted everything to be even more interconnected - so I added a mechanic to alert the horde to our presence

Now as long as the level was simple this worked fine and it looked ok, so I just left it at that, but now that my intro level has taken shape and I have placed more zombies the fact that zombies were alerted on the other side of walls just looked wrong, so I decide to fix this

The first step towards that is a simple LineOfSight check, first I find the zombies within a certain radious, then I filter those based on if they can see the player, now at the moment it works when you hit a zombie, but the next step is just hooking it up to shooting, so that shooting alerts nearby zombies that can spot you

Here is a demo - red lines means they can see you, white they can't: