CMCA members, Don and Elizabeth Jamieson did their own conversion and as a result developed this excellent security screen idea - see review on this page. The biggest problem with all window screens is access for cleaning the outside of the windows. Don solved this in a unique way by running a piano hinge right across the top of the frame. He choose security mesh as neither of them liked the fenced in by bars look. Special headed screws prevent intruder access. You could of course replace these with a keyed lock quite easily.