Attentive, watchful (9)
I believe the answer is:
observant
I believe this clue is a double definition.
'attentive' is the first definition.
(similar in meaning)
'watchful' is the second definition.
(I've seen this before)
(Other definitions for observant that I've seen before include "diligent in duty" , "Good at noticing" , "with a keen eye" , "Quick to notice things" , "Orthodox" .)