So I've gone back to trying to get into BG. Last time around I tried to play a Good-Aligned Paladin in keeping with the high fantasy trappings of the setting. That didn't exactly go well, so this time I rolled up a Neutral Evil thief who operated more like a protagonist from a crime novel (i.e. doing petty theft as needed and pulling B&E jobs for a more lucrative haul,but otherwise helping people out to get rewards and build a name for myself as someone who my future and present clients could count on). Upon realizing they were leaving Candlekeep, the first thing that came to mind was to start "acquiring" assets that noone would be able to link back to me taking in order to get the funds to buy studded leather, a longsword, and a shortbow with scratch to spare, along with any other spare equipment I could find. I looted the rooms in the inn not occupied by awake people, and made out like a bandit, but when I got to the infirmary, I found that once I so much as accessed a lockpicked cabinet, the NPCs would call the guards after seeing me, even if they saw me after I had moved far away from the desk and they did not have a line of sight on the desk. Is this some kind of bug, or am I missing something?

EDIT: got nijaed by TrollumThinks!!

Not sure, but you might try hiding in shadows first before opening the cabinet, or coming back at different times of the day to see if the infirmary is deserted before looting the cabinet. I wouldn't waste too much time with it though. I've heard rumors of a cave with untold treasure guarded by Flesh Golems near a lighthouse. And they say Winter Wolf hunting in the wilds of the southern provinces is very good for both profit and experience.

I also remember reading about an exploit/bug where you can keep the possessions of the "illusion" party members after the combat tutorial in Candlekeep.

Actually, I've been able to steal from there without the guards being called. Had to be really patient to be certain no one could see me, but was able to do it. There are a couple people in there and they can see you from almost all angles. Your best bet is to move the rest of your party in a such a fashion that it blocks at least one of them from moving and then wait until the other one is in one of the rare blind spots.

Alternately, I believe if you put your party near the door and then steal with your thief, immediately pause, select the whole party, then transition out the door, this will drag everyone out before the guards can arrive. I did this a number of times when looting houses when the owners could see the chest I was trying to loot.

So, the trap is silent and undetectable, but it only summons the guards when I am seen after the fact?

Save scumming it is, then. The initial hassle is bad enough, but if I need to go back to an area I've stolen from, then it's the whole song and dance all over again to try and avoid NPCs who will immediately pin me for stealing something that went missing an hour ago.

The trap is quite specific. Here is the decompiled script:

===================
IF
Opened([ANYONE])
Range([PC],2)
See([NEUTRAL])
General(LastSeenBy(Myself),HUMANOID)
!StateCheck(LastSeenBy(Myself),CD_STATE_NOTVALID)
!See("WatcherEnforcer")
!See("FlamingEnforcer")
!See("AmnishEnforcer")
!See("Guard")
!See("HouseEnforcer")
!GlobalTimerNotExpired("abCalledGuards","GLOBAL")
!StateCheck(LastTrigger,STATE_INVISIBLE)
!StateCheck(LastTrigger,STATE_IMPROVEDINVISIBILITY)
THEN
RESPONSE #100
SetGlobalTimer("abCalledGuards","GLOBAL",12)
DisplayString(LastTrigger,9896) // Someone has noticed you! You hear the guards being summoned!
Wait(3)
CreateCreature("WATCHN",[-1.-1],0) // Watcher
END
=======================

What this is doing is watching for the container to have been opened, AND the PC being very close to it and visible, AND the container can be seen by a neutral humanoid. If those conditions are met, the guards are called. This means that you MUST go invisible, OR get out before the priest walks into LOS with the container (NOT the PC).

TL;DR, he's not looking for your character, he only reacts if he sees the container has been broken into and opened, and your PC is at the scene of the crime. Makes sense to me.

The idea of the NPCs calling the alarm after seeing a looted chest is one thing (Thief the Dark Project did something similar in one mission), but the NPCs called the guards after seeing me, not the chest. Furthermore, if I need to go back to an area days later (like, say, the Friendly Arm to try to return some quest items), then it seems like I am still at risk for triggering the guards.

No they didn't. It may have seemed like that to you, but the script simply does not work that way. No you're not. Guards that are called to an area stay there for a number of in-game hours. If you go away and come back the next day, the area script will call DESTROYGUARDS and they will disappear. The script on the trap triggers only once, and never when you go back.

All I know is that I picked the lock safely (not that the NPCs seemed to care about seeing that, but I always waited until I was clear anyway), pilfered the desk, and walked out before the NPCs could have moved. I do have the UB mod installed, so maybe that changes the script, but I didn't see that listed as one of the fixes; if that isn't the case, then I think this would raise concerns as to a bug in my copy, because short of me figuring out how to record a clip, all I can offer you is my assurance that they never saw the desk after I had freed it from the burden of a healing potion. Perhaps I should rephrase; if I go rob a chest, go invisible and leave before the guards are even called, what is stopping the NPCs from calling the guards when I come back if I leave before the script triggers? It seems like the script would trigger regardless of how long ago the chest was robbed, meaning I could come back a week later and have to deal with this if that's the first time they notice the chest is empty, I am in close proximity while visible.

If you leave before the guards are called, then they will never be called. If the trap has been triggered and you leave, they have already been called -- if you see the message. They cannot be called AFTER you leave. The script ONLY runs while the player is in the area. If the trap has been triggered and you leave, then come back a week later, as I said previously, the guards' time will have run out, but the script will never be called again.

Edit: For clarity, trap scripts run once, and once only.

So if I pick, loot, leave before the alarm is raised, then come back later, the script will not trigger once they see the chest after I get back? Thank the Lady for small favors.

That said, does it matter if the NPC in question is asleep? I looted a chest in the room of a sleeping elf at the Friendly Arm and raised the alarm at once; I don't see how they could have possibly seen me if they were unconscious on their bed, but the script doesn't seem to make that differentiation.

Yep, come back later and you're safe.

A sleeping NPC can either be scripted into the trap or not. Some, like the sleepers in the FAI, will notice you. It's best to loot that place during daylight hours. Not all traps are the same, just like not all locks have the same difficulty.

Le sigh. I was hoping that I would be able to avoid metagaming this time around, but it looks like I'll be resorting to save scumming. The idea of a trap alerting people is one thing, but when it is made undetectable and acts like this, it seems like it is trying to simulate the NPCs catching you in the act, even if they couldn't possibly be doing that (i.e. person keeps sleeping even when they "catch" you stealing).

Ah well, at least I can look forward to exercising self defense against Minsc.

I would question how feasible that would be, but my familiarty with code language is limited, so looking at the code will quickly go nowhere. However, there were at least two good options to go with here: (1) have looting not wake up sleeping people, either at all or if the PC fails a die roll against Move Silently or Dexterity, or (2) design an engine from scratch that will let you do what you want to do as opposed to recycling an engine from a planned RTS game (Battlefield Infinity) that already has certain constraints (to say nothing of its various other flaws) in place that interfere with the game the designers are now trying to make; it's like they had started making a square peg and started sanding off the edges to try and make it fit into the new hole they wanted it to go into, but they could have saved themselves a lot of bother by just making a round peg from the start since the result they went with snagged on the hole partway through.