siren vs alarum

siren and alarum both are nouns.

Word	Noun	Adjective	Verb	Adverb
siren	Yes	No	No	No
alarum	Yes	No	No	No

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

Other hypernyms of siren include alarm, alert, warning signal.

siren (noun)	alarum (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