automobile horn vs alarm system

automobile horn and alarm system both are nouns.

Word	Noun	Adjective	Verb	Adverb
automobile horn	Yes	No	No	No
alarm system	Yes	No	No	No

As nouns, alarm system is a hypernym of automobile horn; that is, alarm system is a word with a broader meaning than automobile horn:

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

Other hypernyms of automobile horn include alarm, warning device.

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