Father needs new security alarm, perhaps (5)
I believe the answer is:
siren
'security alarm perhaps' is the definition.
(a siren is a type of alarm)
'father needs new' is the wordplay.
'father' becomes 'sire' (synonyms).
'needs' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'sire'+'n'='SIREN'
(Other definitions for siren that I've seen before include "Alarm; temptress" , "Device making a loud wailing sound" , "Temptress - makes a loud noise!" , "Warning signal generator" , "Alarm - charming female" .)