Of course, I know this only applies to my home and my dog, but it would be possible to either climb out a window, or walk right out the door, and not wake my dog, even if the person made a little bit of noise when they were doing it.
At night, when we go to bed, so does he, and he usually chooses to sleep in the laundry room, away from all of the windows and all three entry floor doors. He is also used to the sounds of two cats playing and getting into things all night, and the sounds of kids getting up to go to the bathroom, get a drink, or rolling out of bed on rare occassion. it wouldn't take a lot of noise to wake him up, but a hushed voice, a small cry, or a quiet footstep wouldn't necessarily wake him up, unless a stranger entered the room he was in.
Dogs aren't infallible. They have to sleep, too.