Louvered windows are not so common as they used to be. In the main, this is because their inherent lack of security is well recognised. There are some measures that can be taken to make them less vulnerable, but these should be seen only as temporary, for overall, it is best to replace them at the earliest opportunity. Some are made with the glass secured in the frame. If not, fix the glass in both frames with an epoxy resin adhesive. If the windows are sited in a vulnerable position, you may need to fit a grille or bars, though the better option would be complete replacement.