WindowAlert Modern Square UV Decal helps prevent wild birds from accidentally flying into your windows. This innovative decal features a special coating that reflects ultraviolet sunlight, which is invisible to humans but appears as a bright glow to birds, similar to a stoplight. To use, simply apply the decal on the outside of your window. For results, concentrate the decals in the center and then work outward, placing them at least every two feet across the glass. Scientific studies recommend spacing the decals two inches apart horizontally and four inches apart vertically to provide maximum protection for your windows. Model Number: