on the qui vive vs alertness

on the qui vive and alertness both are nouns.

Word	Noun	Adjective	Verb	Adverb
on the qui vive	Yes	No	No	No
alertness	Yes	No	No	No

As nouns, on the qui vive and alertness are synonyms defined as:

Other synonyms of on the qui vive include sharp-sightedness.

on the qui vive (noun)	alertness (noun)
lively attentiveness	lively attentiveness
	the process of paying close and continuous attention
	a state of readiness to respond