alert vs unalert

alert is a noun but unalert is not a noun.

Word	Noun	Adjective	Verb	Adverb
alert	Yes	Yes	Yes	No
unalert	No	Yes	No	No

alert (noun)	unalert (noun)
a warning serves to make you more alert to danger
an automatic signal (usually a sound) warning of danger
condition of heightened watchfulness or preparation for action

alert (adjective)	unalert (adjective)
engaged in or accustomed to close observation	not alert to what is potentially dangerous
mentally perceptive and responsive
quick and energetic

alert (verb)	unalert (verb)
warn or arouse to a sense of danger or call to a state of preparedness