#2 is a pretty sound sleeper. Our apartment has really thin walls, and we have noisy neighbors. She also has a pretty loud big sister.
However, there are certain very quiet sounds that she easily wakes up to. The hardest one for me: the sound of my jeans swishing as I walk. You see, I am not a super skinny girl. My thighs touch. I'm good with it. But when I walk, if you really listen, you can hear the denim of my shorts swish. This is a problem because #2 still sleeps in my room. In our home, you always have to go through a bedroom to get to a bathroom. If #1 is asleep, I can't go use her bathroom, because the door sticks and wakes her up. #2 can easily sleep through the squeaky bedroom door, the closing of the bathroom door, all noises made in the bathroom (like hand washing and flushing toilets) all of that. However, the sound of my jeans wakes her up. I have now adapted with this really awkward walk where I space out my legs and squat down a little so as to not let my jeans swish.
I just ran through her room to get my phone that was ringing. (She won't sleep through that.)
I think I pulled something doing my awkward "don't let the thighs touch" move.
The things we do for our kids. ;)