alarm vs red flag

alarm and red flag both are nouns.

Word	Noun	Adjective	Verb	Adverb
alarm	Yes	No	Yes	No
red flag	Yes	No	No	No

As nouns, red flag is a hyponym of alarm; that is, red flag is a word with a more specific, narrower meaning than alarm:

alarm (noun)	red flag (noun)
a device that signals the occurrence of some undesirable event	something that irritates or demands immediate action
a clock that wakes a sleeper at some preset time	a flag that serves as a warning signal
an automatic signal (usually a sound) warning of danger	the emblem of socialist revolution
fear resulting from the awareness of danger

alarm (verb)	red flag (verb)
warn or arouse to a sense of danger or call to a state of preparedness
fill with apprehension or alarm; cause to be unpleasantly surprised