Hello I've had windows fitted. The top third is static and the bottom two thirds opens outwards. There isn't a way to fix them so they don't blow too far open in windy weather. As I have a cat and don't want it to fall, I've attached a chain to the handle on window and attached it to a hook on windowsill. Any ideas of a better way to do it please?

 

Window screens or window guards can be installed. Most modern windows that open come with screens. Window screens tend not to be sturdy enough to prevent a child from falling, but may deter a cat from exiting. Window guards, used for childproofing windows tend to have a minimum of 4"-spaced bars and would not restrain a frisky cat. There are window guards available that prevent window from opening more than 4" but 4" might not deter a cat attracted to another outdoors or a bird. Safety netting over window could be an option.

It sounds like you have come up with an excellent solution if cat can not get out. It is unfortunate that windows open only from bottom & not top. Avoid placing furniture near windows because furniture tends to encourage cats to climb. Spraying window sills with pet repellent may deter cats from climbing on window sills. There are the old-fashioned window screens available that can be expanded to fit window width. These can be inserted in window frame on interior and removed as needed.