Breakdown of Собака не должна лаять ночью, а то разбудит людей.
не
not
собака
dog
люди
people
ночью
at night
Questions & Answers about Собака не должна лаять ночью, а то разбудит людей.
What exactly does а то mean here, and can I just use иначе instead?
а то is a colloquial but very common conjunction meaning "otherwise" or "or else." It specifically introduces a negative consequence, warning, or threat. You can use иначе (otherwise) here, but а то sounds much more natural in everyday spoken Russian for this kind of warning.
Why do we use the imperfective verb лаять (to bark) but the perfective verb разбудит (will wake up)?
не должна лаять uses the imperfective because it expresses a general rule or ongoing prohibition (dogs shouldn't bark in general). However, разбудит is perfective because waking people up is seen as a specific, one-time result or consequence of the barking.
Why is the word for night, ночь, written as ночью here?
ночью is the instrumental case of ночь. Russian uses the bare instrumental case without a preposition to indicate the time of day when an action regularly happens, translating directly to "at night" or "during the night."
Why isn't there a pronoun before разбудит? Shouldn't it be а то она разбудит?
You could include она (she/it), but it is completely optional. Russian frequently drops subject pronouns in the second half of a compound sentence when the subject (in this case, собака) hasn't changed from the first half.