I agree with the sentiment here; there seems to be an impression that a baby monitor is a safety device. I'm not sure it is.

We use a baby monitor during naps and overnight. It's a good way to relay any noises and reassure us he's ok, but you can't really see enough detail on an overhead camera to see they're breathing or anything like that. It failed a few nights ago, and we woke up when we heard the crying through the couple of doors. (If we were awake, downstairs and it failed, we would have tried to fix it pretty quick, but we have the fairly basic backup strategy of going to sit upstairs with him.)