Remember, a criminal can break a window and open it from the inside. If a window lock is fitted, this will not be possible. If you like to leave your windows open you should install a window grille or window bars. Ensure that they are securely fastened into the surrounding masonry. If you have a balcony, make sure that the balcony door cannot be opened from the outside.
Locks are available for sliding balcony doors and are easy to install.