observant

Having or showing keen perceptiveness; perceptive.

Diligent in observing a law, custom, duty, or principle.

Watching; watchful; observing; having or characterized by good powers of observation, or attention, care, accuracy, etc., in observing.

Attentive; obedient; submissive; ready to obey and serve; hence, obsequious: with to or of before a personal object.

Carefully attentive in observing or performing whatever is prescribed or required; strict in observing and practising: with of.