To notice a group of nearby PCs - Perception + Alertness, Difficulty 6
To hear normal conversation across a noisy room - Perception + Alertness, Difficulty 8
To slip through a door behind someone while using Obfuscate - Dexterity + Athletics, Difficulty 8
To read someone's emotions / detect a lie - Perception + Empathy, Difficulty 6; Resisted by Manipulation + Subterfuge, Difficulty 6