[Action]
[ he does indeed notice her - well, he smells her, but doesn't see her. his back is to her, but that scent is unmistakably hers, and that tingly slayer-is-near presence gives her away, too. the afore mentioned scent rules out any faith possibilities. not knowing that she has ear buds in, he speaks up, thinking he's called her out on trying to sneak up on him. ]
You know I can smell you.
[ ... ]
Buffy, what are you-- [ he stops mid-technique and drops his hands, whirling around to face her. ] Oh. [ angel shakes his head and walks over to her, gently pulling one of ear buds free. ] Trying to sneak up on me?