Sound alarm until danger is over initially (5)
I believe the answer is:
audio
'sound' is the definition.
('audio' can be a synonym of 'sound')
'alarm until danger is over initially' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'alarm until danger is over' is 'AUDIO'.
(Other definitions for audio that I've seen before include "shown in reproduction" , "Prefix relating to sound" , "TV sound" , "Television sound" , "Electronic sound reproduction" .)