Drill an angled hole through the top frame of the lower window partially into the frame of the upper window. The insert a nail or eyebolt. The window can't be opened until you remove the nail. Make a second set of holes with the window partly opened so you can have ventilation without intruders. Lighting Lighting is one of the most cost-effective deterrents to burglary.
Indoor lighting gives the impression that a home is occupied.
If you are going to be away from your home, consider using automatic timers to switch interior lights on an doff at preset times. Outdoor lighting can eliminate hiding places. Install exterior lighting near porches, rear and side doorways, garage doors, and all other points of entry. Entryways to your home always should be well lighted. Place lights out of reach from the ground so the bulbs cannot be removed or broken.