The parent not caring for the baby learns to sleep through. My wife and I swap roles when we wean babies, we need just a couple nights to get used to the changed role.
Sleep through baby crying? I found my own babies cries to be a complete NMI.
When we had infants I'd go back to sleep pretty well instantly (co-sleeping, with baby on a side-cot at bed level; baby breastfed, not by me) but in general one would wake to the little snuffles that precede the crying (I guess that helps to calm them before they get in a tizzy [in a state, brought on by their own actions, crying in this case]).
I sleep through thunderstorms without stirring.
I'm a few years out from dealing with crying babies and still if there's crying in the background, that sounds like one of my kids, I'll pop-up like a meerkat. The sound even gets though (non noise-cancelling) headphones when I'm gaming, though I won't know what I've heard until I take them off.
It helps if the father is a night owl who works from home. Back when we had a baby (20 now) I preemptively bottle fed her at 2 am. She didn't wake up other than sucking from the bottle. Neither did her mother who was sleeping next to her.
When we had infants I'd go back to sleep pretty well instantly (co-sleeping, with baby on a side-cot at bed level; baby breastfed, not by me) but in general one would wake to the little snuffles that precede the crying (I guess that helps to calm them before they get in a tizzy [in a state, brought on by their own actions, crying in this case]).
I sleep through thunderstorms without stirring.
I'm a few years out from dealing with crying babies and still if there's crying in the background, that sounds like one of my kids, I'll pop-up like a meerkat. The sound even gets though (non noise-cancelling) headphones when I'm gaming, though I won't know what I've heard until I take them off.