If I hear a skeleton, or a zombie, how far away could he be? Obviously he can be right next to me, but what is the largest possible range?
I've done some testing, and it seems that it is 16 blocks, from the mob's head to yours. I tested by encasing a pig with dirt, but I assume that it's the same for all mobs. Except Ghasts, that is. It's definitely longer there, probably 100 blocks.
BTW, yes, the pig is perfectly fine except for the time I accidentally hit him, and the time that he got shot by a skeleton.