How about a Killer version of Alert
There quite a few perks for Survivors to track the Killers movement. The strongest are Spine Chill and Alert. Alert is very useful, since a Killer will break a pallet or kick a gen. So how about the Killer gets a similar perk? If a Survivor misses a skill check, his aura is revealed for 5 seconds to the Killer.
I think this an awesome idea ;)