We usually close the 1st floor windows well before we go to bed because it's always cool on the 1st floor and will get chilly even in the summer if the windows are open after dark. Honestly, DH usually does it and I don't know if he locks them or not. That said, all the ones that we open (on the one side and back of the house) are high enough off the ground that I could just barely peek into them or way too high to reach.
We do lock our doors at night when we go to bed, but we never lock the house during the day whether we're home or not.
We also lock the cars at night. We and our neighbors have had teenagers go into them right after school gets out for the summer. They've never done damage or stolen anything valuable, but we would like to avoid any future incidents.