warning device vs alarm system

warning device and alarm system both are nouns.

Word	Noun	Adjective	Verb	Adverb
warning device	Yes	No	No	No
alarm system	Yes	No	No	No

As nouns, warning device and alarm system are synonyms defined as:

warning device and alarm system: a device that signals the occurrence of some undesirable event

Other synonyms of warning device include alarm.

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