Surprise Rounds: Perception DC?

[Uwotm8]

In the Combat chapter and perception skill description, calls for perception checks are referred to but it gives no advice for a set DC or even opposed checks between either perception or stealth. Which is it? There is a mention of aware versus unaware. However, you can be aware of an actor and not aware if their intent is hostile. I would still think a perception check is called for if someone tried to randomly attack you if you had no reason to believe they would before hand.

[Chemlak]

Thank goodness for GMs.

Take a look at the perception ranges given in the Environment section of the CRB for an idea of maximum perception ranges, and consider bluff/sense motive for close range surprises.

[Uwotm8]

I'd like a rule on it better. :) Failing that, guidance on what and when would be good, too.

[Dragonsbane777]

I found this system in these forums a while ago, it works well.

Determine Awareness: Perception (one roll for group, highest mod) vs DC 20 (PCs are travelling fast), 15 (PCs at normal travel), 10 (PCs travelling slowly) or Stealth of enemies (use lowest modifier). Do the same for enemies in the other direction.

Determine Max Distance:
Forest:
- Heavy 2d6 x10 feet
- Medium 2d8 x10 feet
- Light 3d6 x10 feet

Desert: 6d6 x10 feet

Plains 6d6 x40 feet

Mountains: 4d10 x10 feet

Hills:
- Gentle 2d10 x10 feet
- Rugged 2d6 x10 feet

Rain/Snow ½ range

The difference in the check x5 feet gives the distance they are aware / see the other group.

Example:
Awareness PCs: Perception of the ranger, highest mod of the group, gives a result of 18, vs the lowest Stealth of the orc group (a clunky fighter would give them away, but they are all sneakers), a 21. The players are unaware and could be surprised.

Awareness Orcs: The orcs get a Perception roll of 19 and the PCs are travelling normal speed, so they beat the DC of 15. The difference is 4 (19 - 15) so the orcs see the PCs at a distance of 20 feet. Had the orcs gotten a higher roll, a 29 for instance, then they would have seen the PCs at up to 70 feet.

Encounter Distance: They are in a heavy forest, and get a max distance result of 50 feet. With their high roll above with a range of 70 feet, the distance would be reduced to 50, as that is the max distance rolled.

This gives you awareness and distance, although it is a tiny bit confusing and tedious at times.

[dragonhunterq]

In the case of being aware of someone but not aware of their hostile intent, you can use bluff or sleight of hand to set the perception DC.

[Malag]

I always use Stealth modifier from a monster while it's taking 10 on Stealth check. It gives me quick and easy DC when I need it. I believe several authors in PFS scenario's use the similar conclusion. If there is bigger distance involved, add -1 penalty for each 10 ft. of distance on Perception checks. Social encounters might include Bluff or Sleight of Hand checks as already mentioned.