As you're moving your head and eyes around, sneak looks at the girl that you want to check out. [substeps] For instance if you notice her at a sporting event, you can pretend to watch the game but steal looks at her instead.
[header] How to check out a girl without her noticing [title] Shift your gaze around. [step] Staring makes it obvious that you're checking a girl out. Instead of keeping your eyes on her, pretend like you're looking around the room naturally.