How do you guys handle players with really high passive perception? I have one that got the Observant feat and high Perception already, giving them 21 Passive Perception at level 1... How the hell do I deal with that!? They spot everything at all times...
As [MENTION=97077]iserith[/MENTION] said there are some options with asking a player to state what they are focused on.
I've had one player play a character that was a knowledge cleric and rogue with expertise in perception. She likes watching Sherlock Holmes and Elementary, as do I, so we both understood the expectations that the character will notice a lot of things without specifically stating what the character is looking for. She would not be able to play in Iserith's games because she would expect that the DM will feed her info that her character would notice without the player specifically saying what she is looking for. So that is what I did. However; I gave the player information that the character would perceive. A hidden door is a discontinuity in the wall or a series of cracks in the wall that is vaguely dwarf sized. A trap may have the indicators of dried blood, small holes in the decorations on the treasure chest, or notice that the dust on a stair case is lighter in the center than on the perimeter. The player now has new information to work with, but they still don't know how the hidden door works or how the trap triggers. In my game figuring out how a dwarven hidden door in masonry or stone works requires significant investigation. After the rogue identifies that there is a trap, well they may need to disable it or us the barbarian trap detection and disable method.
With respect to NPCs hiding I like to use a passive stealth score. Although the PH indicates a stealth check is rolled and compared to a passive perception, it also states that repetitive use of a skill can be defaulted to a passive score. So, when setting up a dungeon ambush, I'll allow the bugbears or goblins a chance to use their passive stealth score if they have a blind and ambush set for intruders. If there are two NPCs working together then they can assist their buddy and it's a passive stealth score with advantage. I will roll a stealth check if the NPCs move from their blind and do not get a
couple minutes to setup a new hiding spot and use the passive stealth.
How has this played out? I have a few examples. 1) The character was busy investigating a liches library while the warlock in the party was also busy looking at a few prized books. I clearly stated that the books had a heavy layer to dust, cob webs, some white dust similar to chalk laying near the books. The warlock still picked up the books and breathed in the white chalk which was part of a trap. 2) While investigating a room it was very clear to the cleric character that a door was on a stone wall; but no other character could clearly make it out with a roll or passive score. The cleric character could not roll high enough on an investigation check to figure out how to open the door. 3) There have been a few times when the character finds the traps on a chest and succeeds in disabling them without risk. This is what the player was hopping to do.
I should mention, that if the player roll lows on the first attempt I may fail forward, or I may increase the difficulty slightly. In general, if a player asks to roll again, with out stating a new approach I feel is different enough from the first I increase difficulty by 2. If there is request for a 3rd roll with out a change in approach then I increase the difficulty by 5. I increase the difficulty by 5 for each subsequent roll and I tell the player that their character is starting to become frustrated and it's getting harder to solve this task with the same approach. Generally, at that point, they pass the task off onto another player, who needs to state a new approach, or they give up. This typically happens with lock picking and trap disabling.
A highly observant character in the group can be a lot of fun for the group. If you like the Sherlock Holmes stories, it may be a good idea to watch a few an get an idea of what a highly observant person may notice.