Another word for observant
Given to observing
keen, alert, penetrating, wide-awake, discerning, perceptive, sharp, eager, interested, discovering, detecting, discriminating, searching, understanding, questioning, deducing, surveying, alive, contemplating, regardful, considering, sensitive, clear-sighted, comprehending, bright, intelligent, on the ball*, on the beam*, on one's toes*; see also intelligent 1, judicious.
Engaged in observing
watchful, gazing, attentive, alert, awake, wide-awake, sleepless, wakeful, noticing, viewing, vigilant, reconnoitering, guarding, mindful, on guard, regardful, listening, heedful, on the watch, on the lookout, on the qui vive, looking out, intent on, alive to, careful, undistracted, intent, open-eyed, sharp-eyed, circumspect, cautious, wary, prudent, marking, inspecting, scrutinizing, examining, surveying, all ears*, all eyes*; see also watching.