The Collaborative International Dictionary
To be on the qui vive
Qui vive \Qui` vive"\ (k[-e]` v[-e]v"). [F., fr. qui who + vive, pres. subj. of vivre to live.] The challenge of a French sentinel, or patrol; -- used like the English challenge: ``Who comes there?''
To be on the qui vive, to be on guard; to be watchful and alert, like a sentinel.
Usage examples of "to be on the qui vive".
As I remember the New England boy (and I am very intimate with one), he used to be on the qui vive in the spring for the sap to begin running.
I think it would behoove us to be on the qui vive for any such developments.