This requires both client and server hooks in order to be remotely effective, which promotes bad add-on design. Generally client sided add-ons should be avoided because they have a much higher chance of conflicting with other client add-ons and spamming your console + it's just bad design to force people to manually download other files just to access your server. I'm sure someone could make something that says how many enemies are nearby on server side only but that's kind of limited and footstep mods are a more thematic choice