Crossword Genius

Drinking, right, but remaining vigilant (2,3,5)

Ross

I believe the answer is:

on the alert

I'm a little stuck... Click here to teach me more about this clue!

'vigilant' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for on the alert that I've seen before include "vigilant" , "Looking out" .)

I've seen this clue in The Guardian.
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