siren vs warning signal

siren and warning signal both are nouns.

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

As nouns, warning signal is a hypernym of siren; that is, warning signal is a word with a broader meaning than siren:

Other hypernyms of siren include alarm, alarum, alert.

siren (noun)	warning signal (noun)
eellike aquatic North American salamander with small forelimbs and no hind limbs; have permanent external gills	an automatic signal (usually a sound) warning of danger
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