Shock call centre with gun (5)
I believe the answer is:
alarm
'shock' is the definition.
(I've seen this before)
'call centre with gun' is the wordplay.
'centre' says to take the centre.
'with' means one lot of letters go next to another.
'gun' becomes 'arm' (I've seen this in other clues).
The central letters of 'call' are 'al'.
'al'+'arm'='ALARM'
(Other definitions for alarm that I've seen before include "Announcement of danger" , "Warning bell" , "Wake-up call?" , "Frighten, disturb" , "Device to signal danger" .)