I know we were gifted one, and it didn't ever get used.

When the baby was brought home he shared the bedroom with the pair of us, and it was immediately obvious if he was crying.

Later when he moved to sleeping in his own room we could still easily hear the noise of crying, as the room was immediately adjacent to our own, and we left the doors open.

I remember we setup a routine at some point where one of us would sleep in his room with him, leaving the other one free to sleep through the whole night.

Maybe if you live in a mansion, and you can't hear a baby crying from the other wing it might be necessary. But most of the parents I know have always been close enough to hear crying just with their ears. (Although I know there certainly are days, especially early on, where you'll hear but be half-asleep and not really do anything!)

Around here we have a custom of letting your kid have a nap in the baby wagon outdoors, even in winter. I guess people started using baby monitors for that by now. When I was small, mum just left a window a bit open (1970-ish Sweden).

This is even done at daycare down to -15 degrees C. However they do have someone present next to the kids at most times.

There are lots of stories of swedish people going to USA and getting arrested for leaving their kid without supervision outside while being 5 meters away inside a store for five minutes. We are used to a bit more relaxed way of parenting I guess :-)

I'm in Finland (although not Finnish), and we did the same thing. Putting the pram on the balcony, while the child was asleep. We'd usually leave the door partway open so we could hear if he cried.

But to be honest once he was having a nap he was generally predictable, and quiet. Especially the lunchtime naps after food - we knew he'd be absolutely fine asleep for 90 minutes and then he'd probably wake up. On a long day he'd sleep for two hours, but that didn't happen so often.

Interesting reading for people in other parts of the world:

https://www.bbc.com/news/magazine-21537988

Same here in Norway.

Its not necessarily about missing out the crying or not, its about hearing it sooner rather than later. You speak of "the baby". If you got two children, you don't want the youngest crying to wake up the oldest (or vice versa). You really don't want a toddler with a lack of sleep. Its causing temper tantrums extraordinaire. Thus far, I got lucky with ours. When she sleeps, she's gone in la-la land, her brother crying be damned. Or so it seems.