Siren's nose (6)
I believe the answer is:
hooter
This clue is a double definition.
'siren's' is the first definition.
(hooter can mean a siren or alarm)
'nose' is the second definition.
(hooter can informally mean someone's nose)
(Other definitions for hooter that I've seen before include "Car horn or slang nose" , "Gnomon" , "Uphill stone pusher (Gk. myth)" , "alarm" , "Warning sound" .)