motor horn vs warning device

motor horn and warning device both are nouns.

Word	Noun	Adjective	Verb	Adverb
motor horn	Yes	No	No	No
warning device	Yes	No	No	No

As nouns, warning device is a hypernym of motor horn; that is, warning device is a word with a broader meaning than motor horn:

motor horn: a device on an automobile for making a warning noise
warning device: a device that signals the occurrence of some undesirable event

Other hypernyms of motor horn include alarm, alarm system.

motor horn (noun)	warning device (noun)
a device on an automobile for making a warning noise	a device that signals the occurrence of some undesirable event