buzzer vs night bell

buzzer and night bell both are nouns.

Word	Noun	Adjective	Verb	Adverb
buzzer	Yes	No	No	No
night bell	Yes	No	No	No

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

buzzer: a push button at an outer door that gives a ringing or buzzing signal when pushed
night bell: a doorbell to be used at night

buzzer (noun)	night bell (noun)
a push button at an outer door that gives a ringing or buzzing signal when pushed	a doorbell to be used at night
a signaling device that makes a buzzing sound