motor horn vs alarm system

motor horn and alarm system both are nouns.

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

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

motor 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 motor horn include alarm, warning device.

motor 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