Ambulance sound (5)
I believe the answer is:
siren
'ambulance sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for siren that I've seen before include "Loud whistle or sea witch" , "Hooter - femme fatale" , "Loud whistle for sea temptress" , "Seductress" , "Loud warning signal" .)