False alarm ends -- quiet ahead (4)
I believe the answer is:
sham
'false' is the definition.
(thesaurus)
'alarm ends quiet ahead' is the wordplay.
'ends' suggests removing the centre.
'quiet' becomes 'sh'.
'ahead' says to put letters next to each other.
'alarm' with its centre removed is 'am'.
'am' put after 'sh' is 'SHAM'.
(Other definitions for sham that I've seen before include "Mock" , "Mash, being false" , "Not what it seems to be" , "Pretense; bogus" , "imitation" .)