DS1 works shifts. He's very good, barely makes a sound and turn no lights on as he's coming and going, but at certain times of the night all it takes is the click of the front door and I'm awake.
I've got used to most of his shifts and I don't hear him when he's in or out at 1am, but when he's going out at 3:30am or coming in just after 4am, I always wake and by that point of the night I seem to have had "enough" sleep or my mind gets busy so I can't get back to sleep. Then I'm up myself by 6:30.
He's had 4am starts the last 2 days and I'm a wreck!