alarum vs warning signal

alarum and warning signal both are nouns.

Word	Noun	Adjective	Verb	Adverb
alarum	Yes	No	No	No
warning signal	Yes	No	No	No

As nouns, alarum and warning signal are synonyms defined as:

alarum and warning signal: an automatic signal (usually a sound) warning of danger

Other synonyms of alarum include alarm, alert.

alarum (noun)	warning signal (noun)
an automatic signal (usually a sound) warning of danger	an automatic signal (usually a sound) warning of danger