Brief tremor keeping sextet alert? (3,4)

'alert?' is the definition.
(I know that alert can be written as qui vive)

'brief tremor keeping sextet' is the wordplay.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'tremor' becomes 'quiver' (synonyms).
'keeping' is an insertion indicator.
'sextet' becomes 'vi' (group of six - VI are the Roman numerals for six).
'quiver' with its final letter taken away is 'quive'.
'quive' enclosing 'vi' is 'QUI VIVE'.