Let's say for an extreme example I snag myself 28 passive perception. Let's say I'm a level 10 Rogue so.... 10 Base + Perception Proficiency (4) + Rogue Expertise (4) + Observant (5) + 5 Wisdom Modifier = 28.
I know for a fact nothing's gonna be higher than 28 unless someone's criting their stealth rolls. Can I just walk into a room, and out of character choose to not check for traps, not check for secret doors, not check for ambushes, but then my character just notices them all anyway? Can I choose not to even risk rolling below a 10 and just say "I want to use my passive perception." if the DM ever asks me to make a Perception check? Can I walk into a room and tell the DM "I use my passive perception to search for traps."?
I think Investigation would be used more for finding traps and hidden doors. But a super high passive Perception would mean things wouldn't be able to sneak past you, as you said, and I think it would probably negate amubushes, since if I remember right ambushes rely on Stealth checks to some degree.
All of these questions are answerable only by your DM, because passive scores are explicitly a tool that the DM chooses to use or not, at their discretion.
In my game, what it would mean is that you’re very hard to sneak up on and that you get some more detailed (and useful) description when you come into a new environment. There is nothing passive about checking for traps; I would never let anyone use their passive score to actively do something.
99% of the time I really dislike passive scores. I almost never use them as anything other than DCs for other characters’ checks. My philosophy is that if a player wants to do something, they should do it, and if success is in doubt, that means a roll.
The Observant feat is kind of horrible because the rules don't clearly distinguish between when to use active perception and when to use passive perception.
Let's say for an extreme example I snag myself 28 passive perception. Let's say I'm a level 10 Rogue so.... 10 Base + Perception Proficiency (4) + Rogue Expertise (4) + Observant (5) + 5 Wisdom Modifier = 28.
If you are planning to invest that much time and effort into boosting your passive perception, I sincerely hope you have already had a discussion with your DM about the way they intend to play passive perception in their game so that you don't end up feeling unsatisfied with the results of your character build. Because 28 in anything is pretty damn high and if you were a player in my game, I would feel obligated to build my story in a way that let your high passive perception accomplish... something... on a pretty regular basis.
I know for a fact nothing's gonna be higher than 28 unless someone's criting their stealth rolls. Can I just walk into a room, and out of character choose to not check for traps, not check for secret doors, not check for ambushes, but then my character just notices them all anyway?
Ultimately the DM decides whether your character is in a position to notice something in the first place. If the DM decides you need to be within 5 feet of a secret door to have any chance of noticing it and you never go near it, it doesn't matter what your passive Perception is. Likewise, if you're in the front of a 6 man party scouting for traps and ambushes up ahead, the DM can decide you're not in a position to notice a creature that's tailing the group at a distance of 30 feet.
State your intentions and what your character is doing clearly so the DM can decide if you notice something or not. Get in the habit of saying things like "I walk the perimeter searching for secret doors", "I search through all the drawers" or "I pace around looking downwards, checking the floor for traps" rather than "I Perception the room." The latter gives the DM absolutely nothing to work with and when I get requests like that I simply tell the player what their character can spot from where they stand.
Can I choose not to even risk rolling below a 10 and just say "I want to use my passive perception." if the DM ever asks me to make a Perception check?
The DM shouldn't be asking you to make a Perception check unless your passive Perception already failed to notice something, so asking to use your passive Perception is redundant.
You're going to get a wide variety of answers. There's a ton of differing opinions on passive checks, and the main answer is always going to be to ask your DM. But, since it's a question in the Rules Forum, I'll say this: In chapter 5 of the DMG it calls out to specifically use passive perception to notice secret doors. Not so much with concealed doors, as they are hidden from sight. The traps section in the DMG says pretty much the same thing, only the wording is "You can also compare the DC to detect the trap each character's passive perception..." The "can" part of that sentence leads to the notion that passive checks are an optional rule. Nowhere in any of the three core rulebooks is it listed as optional. (But most DMs say it is.) It's always listed as a second way to perceive something. Actually, sometimes it's the first, and actually rolling is listed as the second option. (Like in the secret doors section of the DMG.)
At the end of the day, passive checks are a time saver, and are essentially the 5e version of "taking 10" from earlier editions. If I'm running a dungeon (or house, tower, etc) I use passive perception to determine whether or not the PC's notice something. Because the alternative is that the players are going to search every 5ft square. Especially if you have the mindset of "You're PC isn't searching unless you tell me they are." That's like saying that during combat, you're only looking at what you're fighting... "You didn't tell me you wanted to look BEHIND you also." (Unless you do facing, in which that would apply.)
The other problem is that if you have a 28 passive perception, and your DM lets you use it, you're going to run into a lot of DC 30s to notice things. Hiding stuff from players "Unless they specifically tell me everything they are doing" is one of the last, great "Gotcha" moments from DMs to players.
Let's say for an extreme example I snag myself 28 passive perception. Let's say I'm a level 10 Rogue so.... 10 Base + Perception Proficiency (4) + Rogue Expertise (4) + Observant (5) + 5 Wisdom Modifier = 28.
I know for a fact nothing's gonna be higher than 28 unless someone's criting their stealth rolls. Can I just walk into a room, and out of character choose to not check for traps, not check for secret doors, not check for ambushes, but then my character just notices them all anyway? Can I choose not to even risk rolling below a 10 and just say "I want to use my passive perception." if the DM ever asks me to make a Perception check? Can I walk into a room and tell the DM "I use my passive perception to search for traps."?
Not in my game and likely not by the rules.
Passive checks are used when the DM doesn't want to roll dice OR for tasks done repeatedly. If the character walks into a room and does nothing then the DM may not give them a check since the character is not doing anything that would grant a check.
Perception is slightly different from other skills since, unless you tell the DM you are explicitly doing something else, it is usually assumed that the character is ALWAYS closely watching their environment, looking around them and keeping alert for trouble. Since they are assumed to always be looking around then the DM can use their passive perception to check if they notice anything because it is a task done repeatedly.
If your character chose to stroll along a corridor reading a book or in deep conversation with an NPC or other character, there is a good chance they would notice nothing. The DM would not give a passive perception check because the character is not paying attention. The DM might, if they were feeling generous, give the character an active check to see if they notice anything out of the corner of their eye as they walk along, the DM might put disadvantage on such a check depending on how absorbed the character was in their current activity.
Anyway, the basic rule of thumb is that passive checks don't apply unless your character is taking an action that can be repeated ... perception, investigation, even lockpicking if there are no consequences for failing the check.
P.S. The player doesn't ask for a check, the DM does. So, if you walk into a room, you describe what your character is doing and the DM will then ask for any checks if required. A player doesn't say I walk into a room and make a passive perception check. The player says I walk into the room and carefully look all around at the floor, walls, ceiling and any contents. The DM then either just narrates what they see/find or asks the player to make a relevant ability check. If the DM uses the character's passive perception, the player will likely never know unless the DM plays up how obvious it is to one character and how another character never noticed it.
Passive checks are used when the DM doesn't want to roll dice OR for tasks done repeatedly. If the character walks into a room and does nothing then the DM may not give them a check since the character is not doing anything that would grant a check.
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P.S. The player doesn't ask for a check, the DM does.
I wish I could hit the upvote button multiple time for that one. David42 has it right.
Passive rolls have absolutely nothing to do with anything a character or mob is doing. They simply mean that a player or GM doesn't roll a die (usually for one of two reasons - tension and repetition).
Let's say for an extreme example I snag myself 28 passive perception. Let's say I'm a level 10 Rogue so.... 10 Base + Perception Proficiency (4) + Rogue Expertise (4) + Observant (5) + 5 Wisdom Modifier = 28.
I know for a fact nothing's gonna be higher than 28 unless someone's criting their stealth rolls. Can I just walk into a room, and out of character choose to not check for traps, not check for secret doors, not check for ambushes, but then my character just notices them all anyway? Can I choose not to even risk rolling below a 10 and just say "I want to use my passive perception." if the DM ever asks me to make a Perception check? Can I walk into a room and tell the DM "I use my passive perception to search for traps."?
I think Investigation would be used more for finding traps and hidden doors. But a super high passive Perception would mean things wouldn't be able to sneak past you, as you said, and I think it would probably negate amubushes, since if I remember right ambushes rely on Stealth checks to some degree.
Hombrew: Way of Wresting, Circle of Sacrifice
All of these questions are answerable only by your DM, because passive scores are explicitly a tool that the DM chooses to use or not, at their discretion.
In my game, what it would mean is that you’re very hard to sneak up on and that you get some more detailed (and useful) description when you come into a new environment. There is nothing passive about checking for traps; I would never let anyone use their passive score to actively do something.
99% of the time I really dislike passive scores. I almost never use them as anything other than DCs for other characters’ checks. My philosophy is that if a player wants to do something, they should do it, and if success is in doubt, that means a roll.
The Observant feat is kind of horrible because the rules don't clearly distinguish between when to use active perception and when to use passive perception.
If you are planning to invest that much time and effort into boosting your passive perception, I sincerely hope you have already had a discussion with your DM about the way they intend to play passive perception in their game so that you don't end up feeling unsatisfied with the results of your character build. Because 28 in anything is pretty damn high and if you were a player in my game, I would feel obligated to build my story in a way that let your high passive perception accomplish... something... on a pretty regular basis.
"Not all those who wander are lost"
Ultimately the DM decides whether your character is in a position to notice something in the first place. If the DM decides you need to be within 5 feet of a secret door to have any chance of noticing it and you never go near it, it doesn't matter what your passive Perception is. Likewise, if you're in the front of a 6 man party scouting for traps and ambushes up ahead, the DM can decide you're not in a position to notice a creature that's tailing the group at a distance of 30 feet.
State your intentions and what your character is doing clearly so the DM can decide if you notice something or not. Get in the habit of saying things like "I walk the perimeter searching for secret doors", "I search through all the drawers" or "I pace around looking downwards, checking the floor for traps" rather than "I Perception the room." The latter gives the DM absolutely nothing to work with and when I get requests like that I simply tell the player what their character can spot from where they stand.
The DM shouldn't be asking you to make a Perception check unless your passive Perception already failed to notice something, so asking to use your passive Perception is redundant.
The Forum Infestation (TM)
My general rule is that someone always has to be rolling, so a passive score is only used when your opponent is rolling.
An extremely good rule that I also keep in mind.
You're going to get a wide variety of answers. There's a ton of differing opinions on passive checks, and the main answer is always going to be to ask your DM. But, since it's a question in the Rules Forum, I'll say this: In chapter 5 of the DMG it calls out to specifically use passive perception to notice secret doors. Not so much with concealed doors, as they are hidden from sight. The traps section in the DMG says pretty much the same thing, only the wording is "You can also compare the DC to detect the trap each character's passive perception..." The "can" part of that sentence leads to the notion that passive checks are an optional rule. Nowhere in any of the three core rulebooks is it listed as optional. (But most DMs say it is.) It's always listed as a second way to perceive something. Actually, sometimes it's the first, and actually rolling is listed as the second option. (Like in the secret doors section of the DMG.)
At the end of the day, passive checks are a time saver, and are essentially the 5e version of "taking 10" from earlier editions. If I'm running a dungeon (or house, tower, etc) I use passive perception to determine whether or not the PC's notice something. Because the alternative is that the players are going to search every 5ft square. Especially if you have the mindset of "You're PC isn't searching unless you tell me they are." That's like saying that during combat, you're only looking at what you're fighting... "You didn't tell me you wanted to look BEHIND you also." (Unless you do facing, in which that would apply.)
The other problem is that if you have a 28 passive perception, and your DM lets you use it, you're going to run into a lot of DC 30s to notice things. Hiding stuff from players "Unless they specifically tell me everything they are doing" is one of the last, great "Gotcha" moments from DMs to players.
What a simple and effective way of looking at it.
"Not all those who wander are lost"
Not in my game and likely not by the rules.
Passive checks are used when the DM doesn't want to roll dice OR for tasks done repeatedly. If the character walks into a room and does nothing then the DM may not give them a check since the character is not doing anything that would grant a check.
Perception is slightly different from other skills since, unless you tell the DM you are explicitly doing something else, it is usually assumed that the character is ALWAYS closely watching their environment, looking around them and keeping alert for trouble. Since they are assumed to always be looking around then the DM can use their passive perception to check if they notice anything because it is a task done repeatedly.
If your character chose to stroll along a corridor reading a book or in deep conversation with an NPC or other character, there is a good chance they would notice nothing. The DM would not give a passive perception check because the character is not paying attention. The DM might, if they were feeling generous, give the character an active check to see if they notice anything out of the corner of their eye as they walk along, the DM might put disadvantage on such a check depending on how absorbed the character was in their current activity.
Anyway, the basic rule of thumb is that passive checks don't apply unless your character is taking an action that can be repeated ... perception, investigation, even lockpicking if there are no consequences for failing the check.
P.S. The player doesn't ask for a check, the DM does. So, if you walk into a room, you describe what your character is doing and the DM will then ask for any checks if required. A player doesn't say I walk into a room and make a passive perception check. The player says I walk into the room and carefully look all around at the floor, walls, ceiling and any contents. The DM then either just narrates what they see/find or asks the player to make a relevant ability check. If the DM uses the character's passive perception, the player will likely never know unless the DM plays up how obvious it is to one character and how another character never noticed it.
I wish I could hit the upvote button multiple time for that one. David42 has it right.
Passive rolls have absolutely nothing to do with anything a character or mob is doing. They simply mean that a player or GM doesn't roll a die (usually for one of two reasons - tension and repetition).