Device signalling danger (5)
I believe the answer is:
alarm
'device signalling danger' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for alarm that I've seen before include "uneasiness" , "with which many awake to in the morning" , "Scare or worry" , "Mild panic" , "Consternation: kind of clock" .)