Duh, should've added that that call is also their 'ground predator alert' they'll do that if they see a dog or cat or chipmunk.
Also other hens and roosters will pick up the call if they hear someone doing it.
Some will absolutely start bagoking before they've ever laid an egg. I've had hens that start weeks before they lay their first, though it's normally only a few days to a week early.
You don't need to lock them up to get them to lay in the boxes. When they're getting ready for their first egg...