Speaking from personal experience, the baby’s cry also does a dandy job of waking up the father.
There's even more to it than that.
My eldest daughter was several months old when she learned to stand up at the edge of her crib and her crib had been moved to her own room.
I'm normally a very sound sleeper. I'm talking several standard deviations into "sound sleeper". I've slept through fire alarms.
In the middle of the night I heard the baby making some sounds that I could hear coming from outside our room. A few seconds later I heard a sound as if the baby had fallen to the floor.
Needless to say, I was out of bed like shot to check on the baby. What I found was a baby sleeping as peacefully and soundly as I should have been.
The mystery was solved a week or two later when we discovered an item out of place and on the floor in another room. Evidently a fairly heavy plastic puzzle with a round cross section had been placed in an unstable position on a closet shelf about seven feet above the floor.
Why this item chose the middle of the night to release its potential energy, I don't know. However, the sensation I had at the time was that I had already been awake and had heard the entire sequence of events, which is very unlikely. I think there is a level of awareness even when we are asleep and, if something of consequence happens, we are able to respond.