Comment by bhuber

I take it you've never actually cared for small children. One of the most obvious problems they solve is the ability to go outside earshot of the nursery - doesn't matter if the kid cries if you can't hear them! Besides that, kids often cry temporarily and then go back to sleep like 30 seconds later. It's very convenient to be able to detect if that's likely to be the case without having to walk across the house and open their door.