(a.) Extremely observant; watchful; sharp-sighted.

Argus-eyed advertent agog alert all eyes assiduous attentive aux aguets aware careful concentrated conscious custodial diligent eagle-eyed earnest finical finicking finicky guarded hawk-eyed heedful intense intent intentive keen-eyed lidless listening meticulous mindful nice niggling observant observing on guard on the ball on the job on the lookout on the watch open-eared open-eyed openmouthed prudent regardful sharp-eyed sleepless vigilant wary watchful with open eyes