I thought I understood when to ask players to make perception rolls, but there's a section about spotting a couple of traps at the start of the Starter Set 'Lost Mine of Phandelver' that has confused me
From page 6 "Goblin Trail" (v minor spoilers if you're a PC)
"If the characters are searching for traps, the character in the lead spots the trap automatically if his or her passive Wisdom (Perception) score is 12 or higher. Otherwise, the character must succeed on a DC 12 Wisdom (Perception) check to notice the trap"
Perhaps it's just badly worded - but this states you only get a passive perception check if the characters state they are looking for traps. That doesn't seem right. I thought passive perception was "always on" and a passive check is what you'd use if they WERN'T actively looking for traps
Then it says "otherwise" make an active Perception check - otherwise what? :-
- If they fail the passive check, otherwise get them to make an active Perception check roll
or
- Otherwise they weren't actively looking - make an Perception check roll (and this really makes no sense)
It's making my head go round & round in circles! 
It seems such a fundamental thing to word quite badly at the very start of the advture, esp. as this was intended to hand-hold new DMs. Or maybe I'm just other thinking it! 
Can someone clearly explain checks for spotting traps, when players are actively looking and when they are not?
Thank you!
When actively searching for traps, the lead character is making rolls to find them. If their passive perception is higher than 12, they auto-see it - they automatically see a detail that draws their attemtion to it, even if their perception roll was lower. Otherwise, use the perception roll. In programming terms, it's an EITHER/OR statement: if X (Passive Perception is 12 or over) is True, then condition Y (Auto-see Trap) applies, if X is False then only condition Z (see trap if WIS/Perception roll is 12 or over) applies. In some cases (like actively searching for traps, unless a specific trap says otherwise), it is considered impossible to have a result below your passive perception.
Make sense?
RustedKitsune wrote:
JoyrexJ9 wrote:
OK so
I think I've got it if they are actively looking for traps, but should it be treated differently if they don't state they are?
There is two scenarios as I see it
Player says "I go ahead but keeping an eye out and checking for traps"
- If their passive Percention auto passes check = trap spotted. End
- Else: "DM: Please make a Perception check" If the pass = trap spotted, else = set off trap
Player says "I go ahead up the path" (implies they are not looking for traps)
- If their passive Percention auto passes check = trap spotted. End
- Else: They blunder into the trap setting it off
The reason I think there's a difference, is this would be symetrical with how checks for hiding works
Or should I just treat the two situations the same?
I guess in the end the players will simply state they are going everywhere while always looking for traps! 
In this case I would probably say that if they are not looking for traps they are probably not having perception on the trail, so they automatically fail the saving throw. Have a look at https://www.youtube.com/watch?v=hgNRe76o4_8#t=3525 where Greg Bilsland from R&D DMs the adventure. The link should be to about where the trail section comes up. From the way I interpret what happens the Noble gets a -5 to his passive perception from disadvantage due to distraction (making it 8) and was not looking for traps so he did not get an active roll.
So the "Actively looking for traps" might simply be that you get a roll if the passive perception is not enough.
JoyrexJ9 wrote:
lawrencehoy wrote:
Be3Al2 wrote:
JoyrexJ9 wrote:
It's interesting that the adventure gives the trap a static DC that is compared to the PCs' static Perception score. I was under the impression (based on some of Mike's tweets) that they were going to make it so the DM rolled a Stealth check for things like traps and secret doors and compared it to the PCs' passive Percepetion. I think I may still play it that way myself. Will have to see how it works at the table first, though.
JoyrexJ9 wrote:
As iserith and the Lost Mine of Phandelver state, "If the characters are[n't] searching for traps…" they "don't contribute…to the group's chance of noticing hidden threats" (Basic Rules 0.1, p.65). Invoking the rule of specific beats general, I declare that the example JoyrexJ9 uses is intended as an exception, and the general rule is clear that "the passive Perception scores of the characters…determine whether anyone in the group notices a threat" (p.65). The additional language, "the character [in the lead] must succeed on a DC 12 Wisdom (Perception) check in order to notice the trap," permits about a 40-50% chance to notice one of these traps with an active check even if distracted (the spoiler comes in here, as the player of a character with Wisdom less than 14 and untrained in Perception, can have h/h traipse along foraging or mapping, to exploit this oversight). Rich Baker's been writing modules for a long time, and I think he wanted to make sure that novice players have one more chance to avoid triggering traps at this point in the adventure. This little indulgence of forgiveness will keep anyone from getting excited about lethality (except those who want more of it), as new gamers get used to the logistical aspects of exploration.
Edit: misspelling
We might also be dealing with a scenario specific condition as opposed to an actual rules question.
Based on the rules you could say that a party that's actively searching for traps could use an investigation roll (Int Check) to find the traps. Perhaps the person who wrote the scenario wanted to 'hard code' the concept that the players don't really expect to find traps... that they aren't sweeping the trail ahead with branches, poking the ground with 10' poles, crawling along probing for loose stones, tossing large rocks ahead to set off pitfalls, etc.
The idea would be that the party that's 'keeping an eye peeled for danger' would need to spot something out of place with perception but have a better chance of actually seeing something than a party that's just wandering along, looking at birds and flowers and discussing the results of the World Cup.