warning device vs siren

warning device and siren both are nouns.

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

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

warning device: a device that signals the occurrence of some undesirable event
siren: an acoustic device producing a loud often wailing sound as a signal or warning

Other hyponyms of warning device include automobile horn, car horn, hooter, horn, motor horn, burglar alarm, fire alarm, smoke alarm, horn.

warning device (noun)	siren (noun)
a device that signals the occurrence of some undesirable event	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