Ask your hardware dealer for advice. Double-hung window latches may be jimmied, or pried open. If the window is not used, pin it shut. For windows that are used, drill a downward sloping hole into the top of the bottom window and into the bottom of the top window. Insert a pin or nail.
Louvered windows are poor security risks.
We suggest they be replaced with solid glass or another type of ventilating window. Temporary security can be maintained by removing the window crank. Remember that one window is every bedroom on the ground and second floors must be left available as a fire exit. At night, the bedroom window may often be the quickest and safest means of getting out in case of an emergency. If you decide to sleep with a window open at night for ventilation, leave it only partially open and lock it using a pin.