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Stealing and NPC reaction in BG2
"In Gaelan's house, where you start out, there's a fence upstairs. Neither of them comments on it when you unlock their chests and steal their stuff, right in front of their faces. (You can do this in just about every house in the city, actually. Less realistic, but just as well--it was a huge pain in the last game trying to figure what was fair game to pick up and what would bring the guards storming in.)"
"People in Throne of Bhaal tend to notice and attack you if you open containers in their houses, the way they did in BGI. I don't know why they turned this annoying feature off in Shadows of Amn and then back on now. Save before you snoop--or come back at night, as people in houses often go to sleep in the dark hours."
I have read about it in this articles:
Is it really true? They cut off this npc-reaction features in Shadows of Amn?