alarm vs alarm bell

alarm and alarm bell both are nouns.

Word	Noun	Adjective	Verb	Adverb
alarm	Yes	No	Yes	No
alarm bell	Yes	No	No	No

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

Other hyponyms of alarm include torpedo, air alert, burglar alarm, fire alarm, foghorn, fogsignal, horn, red flag, siren, tocsin.

alarm (noun)	alarm bell (noun)
a device that signals the occurrence of some undesirable event	the sound of an alarm (usually a bell)
a clock that wakes a sleeper at some preset time
an automatic signal (usually a sound) warning of danger
fear resulting from the awareness of danger

alarm (verb)	alarm bell (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