My apartment has windows which are not grilled. They are kept open during the day while I m at home. I close when I go out. My kids don't go near the windows, so it doesn't pose danger to them. I heard that the cats like to climb on things and that's why I was worried and wanted to ask advise from someone who keeps cats cat condos or apartments. Do I need to keep my windows closed at all times or need to install grill before owning a cat?