My daughter moved into a college apartment so I wanted something to help secure her windows without damaging the actual window. This idea will let her open her windows a few inches to let air in but should help keep intruders out. In the case of a fire, she can easily remove the "lock" since it is just held in place by velcro.
Step 1: Collect Materials
You will need inexpensive 1x2 board. Amount will depend on how many windows you want to secure.
Velcro with sticky back: Two strips per window. This can be flexible also. You can buy a long strip and cut it yourself or buy the precut version in a package. I used two, four inch strips of 3/4" velcro.
Paint to match your window sash.
Step 2: Measure the Upper Sash
Measure the top sash of your window. If you want your window to always be "locked" in place measure the entire sash. If you want to be able to open your window a safe distance subtract 5 inches (or whatever opening size you choose) from the total measurement of the upper sash.
Step 3: Cut the Board to Size
Step 4: Paint the Board to Match the Sash
Step 5: Time for Velcro
Cut two 4 inch pieces of velcro or use the pre-cut packaged variety.
Center one prickly piece lengthwise on each end of the board.
Place the soft pieces on the top sash. Place one on the top of the left side of the sash running vertically, the other piece on the bottom, or 5 inches from the bottom to match the velcro on the locking board. Hold the piece of board up to the sash to help you place the velcro correctly.
If you feel that this will not be secure enough, you could place velcro along the entire piece of locking board, or even use the stronger types of velcro. I think it would take some force for an intruder to displace the boar
Step 6: Place the Locking Board
Set the locking board in place. The top or bottom sash can now be opened, but only the distance you have chosen. The board stays in place and if you painted it to match your sash it blends in fairly well. You can remove the board easily to open the window further.