Discussions are good
I like pinning ideas down but I'm always concerned I'll be taken as confrontational.
Part of it is that I was tired when I posted and did not empathize that I was mostly concerned with NPCs and other things that actually make an opposed Perception vs Infultration against the character.
That's it, right there
That was the core missing element to your first post and I just wasn't quite sure which way you were actually leaning. And with that everything else falls into agreement except...(hehe, always an except)...
I think it's this last situation that ARC was speaking about, I just don't want anyone coming away from this discussion thinking that a infiltrator must know where each and every opposed observer (NPC, sensor, or otherwise) is in order to infiltrate successfully.
And I, politely (at least my intent has to come across as polite), disagree for the reasons above. And I would go so far as to say that a player must designate who or what they are trying to sneak past before they roll Infiltration. You have to perceive where the eyes are, and aren't, in order to know how to effectively avoid them, meat-body or otherwise. As a completely absurd and, hopefully, funny example...ever watch a movie with a guy sneaking around. Despite all his best efforts, even if the actor studied with ninjas for a decade on how to be sneaky, why does the audience always see him?
This part I disagree with a bit. If you have ever walked into a room or place and after a minute notice that you DIDN'T notice another person already there, and they are surprised when you say hi to them, to me that shows the ability to sneak by something while unaware of it's presence. Obviously not all things are like that, just the things that require that good old human element, where someone might be distracted or just plain oblivious.
Additionally, noticing something is the responsibility of the person doing the noticing. The perception check needs to be done in order to observe, though situationally this can be drastically modified. If you're not ruling that the person attempting to sneak is "Immediately Noticeable" (I think that's the term the book uses to negate the test), the observer needs to succeed the test, even if the Infiltrater is unaware of the observer.
Anyhow, that's it. I think we agree on most points. And again, I think the perception that I thought you could just waltz in past sensors was because I wasn't clear enough in my original post.
A character rolling a Perception check does not force those in his perception range to roll Infiltration. A character can walk into a room, roll Perception, and notice some or all details. Walking into the room, if the character is intent of finding a particular individual (who isn't trying to hide) then GM would set an arbitrary threshold based on how crowded the room is, other distractions, etc. Where if the target is the only individual in the room, the GM says, "no need to roll, he's there." If there's a dozen or more maybe a threshold of 1 or 2, in a house party 3 or 4, at a Concrete Dreams revival concert 5 or 6 or more. But the sought out individual is passive in this, he's part of the normal scene.
A character trying to sneak around, well, that's a roll that is Opposed. There's a target (or targets) and once designated they are allowed an opposition roll. Take the individual alone in the room. He hears noises from outside the door and so he wants to hide. The GM can say, okay, behind the couch or behind the left curtain at the window which is drawn closed are the two best places to hide immediately (without leaving the room). So the character choose, rolls Infiltration. Now what if someone walks by the window (or a jumped-in drone drops down from the air to peak in, or a sniper across the way looks through his scope, etc.) after the character has hid but before the person(s) on the other side of the door come into the room.
If the character chose to hide behind the curtain, well, his back is against the window in plain view. If the character chose to hide behind the couch, the angle of the couch may be such that he's in plain sight to someone at the window, or half-blocked, etc.
As a GM I would have to say that the hiding character's Infiltration does not apply to the person walking by the window. All that matters is the passerby's Perception against a threshold of 1 if hiding behind the curtain, and 2 or 3 if behind the couch (depending on how much of the couch is blocking the hiding character, maybe higher or just impossible if the character is completely blocked from view). All normal Perception test modifiers still apply to the passerby, of course.
Anyone coming in the room, however, automatically must make a perception test opposed by the character's Infiltration +/- Perception modifiers as normal. The character is trying to hide from them and I would assume that the character is slowly moving around the couch to keep it between him and the target if he chose the couch.
For the crowded party example, in the opposite light. There's a character at the party, it's crowded, and standing near the middle of the room. If the player were to say to me, I want to use Infiltration. I'd have to ask, "against whom?" Certainly not everyone at the party, not the person he's having (or pretending to have) a conversation with. Even with a "slip out unnoticed" kind of attempt, then the modifiers are going to be huge...if he wants to slip out without anyone noticing him. Now, if the character mingles his way towards an exit and then says, "I'm sneaking out," that's different. 1st, he was noticed by some people to have actually been at the party as he mingled his way across the room (they may even remember in what direction he headed). 2nd, anyone facing in his direction (just cause that's the way their standing while talking at the party) would get a bonus to their Perceptions (and anyone standing with their backs to him would have negatives). But ultimately the character is still intent on using Infiltration
against someone or something's Perception.
Now I can see how my original post could be taken as an extreme "player must designate each individual entity they are trying to sneak past" but that was not my intent (or maybe it was and I hadn't thought it all the way through, hehe). In certain situations it's fairly clear; "I'm sneaking across the corporate grounds to the back door." A Perception check on the part of the character will let the GM know whether he notices any or all of the cameras, guards, etc. Then the Infiltration check to set the thresholds for anyone watching those cameras or guards on the grounds. Now if joe-average wageslave comes out the back door, and walks across the grounds over to the parking lot, well, the character would still be using Infiltration against the wageslave so long as the character makes a Perception test to notice the wageslave (which would be pretty easy as the wageslave is keeping to the lighted walkway, opens/closes the door normally, etc.).
But if the character didn't notice a guard on one side of the grounds, then that guard is just going to roll a perception check (with modifiers as appropriate) against a standard threshold because the infiltrating character is using bushes, planters, obstacles, etc. to keep LOS at a minimum between the known threats...which may just put him in plain view to the unknown threats. This works both ways, were a group of ninjas sneaking up on the PCs would get Infiltration vs Perception against all the PCs except the ones they were unaware of. Those unknown-to-the-ninja PCs would get a regular Perception check (with the appropriate modifiers) to notice the ninjas.
To end, all characters are considered to be normally aware and perceiving their surroundings. For characters to notice the obvious it is the responsibility of the GM. At the next level it's the responsibility for players to have their characters to take a moment to actively perceive if they feel there may be something hidden from being obvious. At the final level Players who are actively having their characters sneak around are responsible to designate who or what (even if it's a general whose or whats) in order to let the GM know who he/she's rolling Perception for in the Opposed Test. I haven't come across anything RAW to counter this line of thought. If you have the page numbers or some other examples that would counter this way of thinking, throw'em at me as better here than at the game table and be caught by surprise
