I love to open ours up but I am a little more cautious now. The screens don't do anything. I do shut at least the front ones when I go out. The back windows are in a fenced in area. We have 3 dogs too and if anyone even came near my windows they would start barking. I do shut the one on the side of the house and lock it when I'm not home and also at night since it is one of my daughter's bedroom. We used to have a bunch of kids that would cut through on that side of the yard all day and noght and even though they don't any more I got in the habit. My other DD is afraid to have her window open so when she's in there- she will not leave it open and locks it.
We do live in a neighborhood where everyone notices everything though and if anyone was nosing around at least in the front of the house they would check it out.

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Mom to Katie 1/95 and Sara 5/97