alert

[1]	alarm
[2]	warn , caution , advise , alarm , forewarn , signal , notify

[1]	qui vive
[2]	alerting
[3]	alarm , lookout , warning signal , alarum
[4]	alarm , warning , signal , siren

adj.

[1]	awake , wide awake , watchful , vigilant , attentive , heedful , wary , cautious , on the qui vive , aware , on guard , on the lookout , observant , (Colloq) on the ball , on one's toes
[2]	active , nimble , lively , agile , active , quick , spry , sprightly , vivacious
[3]	watchful
[4]	brisk , lively , merry , rattling , snappy , spanking , zippy
[5]	alive , awake