qui vive

 
Pronunciation: /kiː ˈviːv/

noun

(in phrase on the qui vive)
  • on the alert or lookout: duty requires the earnest liberal to spend most of his time on the qui vive for fascism

Origin:

late 16th century: from French, literally '(long) live who?', i.e. 'on whose side are you?', used as a sentry's challenge