warning signal vs siren

warning signal and siren both are nouns.

Word	Noun	Adjective	Verb	Adverb
warning signal	Yes	No	No	No
siren	Yes	No	No	No

As nouns, siren is a hyponym of warning signal; that is, siren is a word with a more specific, narrower meaning than warning signal:

Other hyponyms of warning signal include torpedo, air alert, burglar alarm, fire alarm, foghorn, fogsignal, horn, red flag, alarm bell, tocsin.

warning signal (noun)	siren (noun)
an automatic signal (usually a sound) warning of danger	eellike aquatic North American salamander with small forelimbs and no hind limbs; have permanent external gills
	an acoustic device producing a loud often wailing sound as a signal or warning
	a warning signal that is a loud wailing sound
	a woman who is considered to be dangerously seductive