I have a 4 month old puppy who's been crate trained since I got her at 7 weeks. She has slept through the night in there since I got her and never barks or whines to come out except one soft bark in the morning sometimes if I sleep in. I started leaving her at home while I work and come home at lunch. I leave her with something to chew on and she doesn't bark or whine when I leave and she seems fine when I come back, like she's just been sleeping all day. My neighbors haven't said anything so I'm pretty sure she's not sitting there barking all day. I also did a practice run with her at my grandparent's house over a long weekend. I put her in her crate upstairs where no one else was and spent the day downstairs or out and about. My dad was there all day and told me she didn't bark except a couple times randomly, but nothing annoying or bad. But there have been a couple of times when I step out of the house really fast like to take the garbage out or get something out of my car and if she sees me walk out the door, she barks and whines. I make sure only to open the door when she's quiet. I've left her while she's napping (in the living room, not in her crate) and I can hear that she wakes up and knows I've left, but she doesn't bark. I come back and she's waiting by the door so I know she knows I left. My question is why does she bark when she sees me leave? Both cases she knows that I have left, but only barks when she can actually see me walk out the door. I don't know how long she'd bark because I usually come right back, but it would be nice to be able to go outside real quick, not have to wait for her to be napping and not have to worry about her barking. Should this be something I actively work on with her or should it eventually disappear as she gets older?