Security changing to all-clear (10)
I believe the answer is:
collateral
'security' is the definition.
(collateral is a kind of security)
'changing to all-clear' is the wordplay.
'changing' indicates anagramming the letters.
'to'+'all'+'clear'='toallclear'
'toallclear' is an anagram of 'COLLATERAL'.
(Other definitions for collateral that I've seen before include "Confirmatory - recall a lot (anag)" , "Money put up" , "subsidiary" , "Aside from the main issue" , "damage?" .)