n. 25B6; adjective
police have asked neighbours to keep alert : VIGILANT, watchful, attentive, observant, wide awake, circumspect; on the lookout, on one's guard/toes, on the qui vive; informal keeping one's eyes open/peeled.
mentally alert : QUICK-WITTED, sharp, bright, quick, keen, perceptive, wide awake, on one's toes; informal on the ball, quick on the uptake, all there, with it.
inattentive.
25B6; noun
a state of alert : VIGILANCE, watchfulness, attentiveness, alertness, circumspection.
a flood alert : WARNING, notification, notice; siren, alarm, signal, danger/distress signal.
25B6; verb police were alerted by a phone call : WARN, notify, apprise, forewarn, put on one's guard, put on the qui vive; informal tip off, clue in.