WindowAlert decals help prevent wild birds from accidentally striking windows. Each decal has a special coating that reflects ultraviolet sunlight. This ultraviolet light is invisible to humans, but birds see it as a brilliant glow much like a stoplight. Place decals on the outside of the window. Concentrate decals at center then work out, placing decals at a minimum, on every 2 feet of glass. For maximum protection, scienti­fic studies suggest placing decals 2 inches horizontal, by 4 inches vertical, from one another. UV coating will fade based on exposure and local elevation. For best results, replace decals every 4 months or test with the WindowAlert UV Flashlight.