Stop Window at a Safe Height Add child safety and home security to home or vacation home or rented cabin by these removable window wedges that stop windows from opening wide enough for children to fall through as well as deter intruders. This window stop installs quickly using velcro type strips: no tools are required. Use two window wedges per window for maximum child safety. Use on double hung, single hung or sliding windows. Note: This product is not a substitute for adult supervision. Never leave a child unattended with an open window . To Install Window Wedge Window Stoppers: Close the window Clean the surface of the window trim prior to application. Do not attach to glass itself. Peel off the backing from the 8 inch loop strip and place in the center of the upper window frame for a double hung or single hung window. Attach the window wedge onto the loop strip at the desired height. Open the window until it is stopped by the window wedge. Note: For maximum child safety, maximum window opening should not exceed 4 inches.