Haunts and Perceiving Them

[Heine Stick]

Characters have a chance to perceive a haunt's presence, as per the Spot entry in haunt stat blocks.

When is the Perception check triggered? My assumption is that the Perception check's triggered when the haunt triggers. That is, in its surprise round.

What's the result of a successful Perception check? Does the haunt not get to go in a surprise round?

[Aranian]

The other way around: characters that perceive the haunt get to act during the surprise round. If they beat the initiative 10 of the haunt with their initiative roll they get to act before the haunt and they could try to disable it with positive energy or simply leave it's area. This requires them to realize it is a haunt, given only the clue after the perception DC. Anyone acting after the haunt can only deal with the aftereffects of the haunt (restraining fleeing friends or heal damage). Anyone affected by the haunt sees its effect.

Example:
The haunt says: Notice Perception DC 20 (to hear the sound of rattling chains) and it's description mentions it affects one room. So the party entering the room triggers the haunt. Everyone rolls perception (DC 20) and all who beat the DC hear the rattling chains. Then the party rolls initiative. Anyone who beat the perception DC and acts on initiative 10 or higher acts (reacting to the sound). Then the haunt's effect materializes: ghosts come out of the walls and fear everyone in the room. Everyone still in the room sees those ghosts and is subject to the fear effect. Now everyone who beat the perception DC but only had initiative 9 or lower acts. Meaning they start running in fear (they didn't save) or acting normally. In the next round everyone acts normally.
Remember that you only get a standard OR move action in the surprise round.

[Heine Stick]

Thanks for the detailed answer. :)