Thanks for clarifying again. I guess I don't see any relevant distinction between "checking" and "looking" at my table where all traps can potentially be noticed without risking triggering them. Any character is going to try non-risky methods first, so I don't see the value (at my table) of asking them to specify whether their approach "checking the lock for traps" involves looking in the keyhole (triggering a Wis (Perception) check) or probing with thieves tools (triggering a non-check resolution based on the mechanics of the trap): it's always going to be the former unless the player is making a mistake that the character would know better than to make.
That makes sense, I can see why you would do it that way.
I don't see a practical distinction between always telegraphing a trap and setting a passive perception DC of 0 to notice the trap. Either way the trap always fails: the primary threat is removed and the trap turns into a terrain obstacle.
Again, telegraphs are missable. My ideal for telegraphs is the “hard but fair” feel of the soulsborne games. Where you may well miss the hint and walk into a trap, but if you do you can easily realize what the hint was. The reaction to falling into a trap, in my opinion, shouldn’t be “damn, if only I had rolled better/had higher passive Perception” but rather “Oh, I should have seen that coming.”
One possible distinction I see would be if you only telegraph traps to PCs, and let NPCs blunder into traps that cannot be detected via Perception and without the benefit of telegraphed foreknowledge. If so the purpose of the distinction makes sense, but it's such an overt form of PC plot armor that I wouldn't be comfortable with it at my table. (For reference, I don't cap a PC-made trap's potential bonus, so NPCs might autofail their Passive Perception checks unlike PCs, but that's a much subtler form of plot armor.)
Well the dungeon’s inhabitants generally know where the traps are, and may well have set them up. I don’t get a lot of PCs making traps. But if I did, or if like the PCs brought an NPC hireling into the dungeon with them or something, yeah, I’d set a passive Perception for them to realize a trap is present, and then have them roll Perception or maybe Investigation to see if they can find how to avoid or disable it. It wouldn’t be very fair for me to have NPCs notice traps without reference to their stats because I actually do know their locations.
I’m also not terribly worried about this method being “PC plot armor.” I’m more interested in creating a desired experience than in preserving ”simulationist” consistency between the rules for PCs and NPCs.
Out of curiosity, do you run a lot of uninhabited dungeons with still-functional, self-resetting traps? The telegraphing methods you describe would only rarely work at my table: almost all my dungeons are inhabited, so the signs of the trap would have been removed when the trap was reset, and the occupants certainly aren't going to advertise their defenses. The rare uninhabited dungeons that were still sealed would have pristine un-triggered traps, and unsealed ones exposed to the elements that might have previously triggered will rarely have been built by a culture with enough engineering expertise to make durable trap mechanisms, let alone self-resetting ones.
Sure, in the exceptional dungeon where it makes sense I'll happily include an already-triggered trap and its grisly outcome, but my motivation for doing so would either be adding flavorful color, or else telegraphing the likelihood of other traps in the same facility. At that point the trap itself isn't a threat.
The idea behind the already triggered trap with the dead person next to it is purely to be a telegraph. It signals that there are traps of this nature in the dungeon and to watch out for them. That kind of thing is likely to be encountered once, early on in a dungeon, but further in you’ll have to rely more on context cues.
I suppose if you need a diegetic explanation for that, the guy who got killed by that early trap was probably an adventurer or other grave robber, but the traps further in are untriggered because other adventures haven’t successfully delved this deeply yet. Or maybe some of the traps are self-resetting, maybe the monsters in the dungeon reset them. It’s not really terribly important to my mind, because again, my goal is to create a desired experience, not a simulation of a real place.
May I ask how you make use of Passive Perception at your table? It sounds like characters with high Passive Perception at your table are no more likely to notice traps than any other characters?
I mostly use passive scores as the DC for actions NPCs take against PCs. So, if an urchin tried to pick your pocket, he’s going to have to make a Dexterity (Sleight of Hand) check against your passive Wisdom (Perception), and on a failure, I’ll narrate his hand making a grab for your coin purse, or give some other kind of clear signal that he’s doing it. If an NPC lies to you, he has to make a Charisma (Deception) check against your passive Wisdom (Insight) and if he fails I’ll describe him stammering, or his voice cracking, or sweat glistening on his brow or something to indicate that he’s nervous.
For a while I did also use Passives to gate telegraphs as well - you’d only feel the draft coming from the secret door if your passive Wisdom (Perception) was high enough, for example. But what I found was that it only served to make certain features of the environment impossible to find. Either I set the DC higher than the highest passive Perception in the group and they would never find it, or I set it lower and play proceeded as described above, where players might or might not find it depending on if they pick up on the hint. Pretty soon I found myself not setting any DCs higher than the highest passive Perception in the group, and not long thereafter I realized there was no point in setting those DCs in the first place.