When NPCs notice something ('Huh...where are you?', 'Who's there?' etc) they don't do anything. In fact they do even less than before they noticed something. They stand around looking in exactly one direction and don't move at all. That is so stupid and boring I can hardly believe it. What would you do if you were a bandit in a world like Oblivion and heard a strange noise coming from somewhere? I would at least look around in all directions and walk around a bit to look in every dark corner next to me.
What I'm looking for is a mod that changes this behavior. If NPCs get in the 'I noticed something' detection state they should walk around looking for the source of the noise. If they don't find anything after a certain time (let's say 10 seconds) they could go back to normal. Would be cool if they would get a torch during that time as well. If you camp in a dungeon you don't run around with a torch on all day long, but you could ignite one if you heard a noise or saw something out of the corner of your eye.
I know that Thieves Arsenal has a similar feature, but afaik it only works for the items added by the mod (special arrows etc).