Observant

Adjective

 * 1) Alert and paying close attention.
 * The too observant police officer noticed that my tax disk was out-of-date.
 * 1) Diligently attentive in observing a law, custom, duty or principle.
 * I was normally observant of the local parking restrictions.

Antonyms

 * introspective
 * nonobservant
 * unobservant

Adverbs for Observant
keenly; aptly; expertly; skilfully; intelligently; acutely; sharply; critically; terribly; dreadfully; alarmingly; officiously; impertinently; impudently; offensively; vexatiously; carefully; watchfully; cautiously; attentively; remarkably; noticeably; alertly; prudently; thoughtfully; meticulously; amusingly; unusually; punctiliously.

Thesaurus
Argus-eyed, active, advertent, agog, alert, all ears, all eyes, assiduous, attentive, aux aguets, awake, aware, careful, compliant, concentrated, conforming, conscientious, conscious, constant, custodial, deferential, devoted, devout, diligent, duteous, dutiful, eagle-eyed, earnest, ethical, faithful, finical, finicking, finicky, guarded, hawk-eyed, heedful, intense, intent, intentive, keen, keen-eyed, lidless, loyal, meticulous, mindful, moral, nice, niggling, obedient, observing, on guard, on the ball, on the job, on the lookout, on the watch, open-eared, open-eyed, openmouthed, perceptive, practicing, prudent, punctilious, punctual, regardful, respectful, scrupulous, sharp, sharp-eyed, shrewd, sleepless, thoughtful, true, vigilant, wary, watchful, wide awake, with open eyes