Millions of wild birds are killed each year flying into windows. Now you can help reduce this loss of life. * WindowAlert is a static-cling decal that may be applied to home and office windows. The decal contains a component which brilliantly reflects ultraviolet sunlight. This ultraviolet light is invisible to humans, but glows like a stoplight for birds. Birds have vision that is up to 12 times better than that of humans. * WindowAlert decals help birds see windows and thus avoid striking the glass. (4 per package). Window Alert decals may be used only on an exterior glass surface - free of any overlay, tinting, film, or coating. Clean glass first with water. Avoid use of chemicals such as ammonia or window cleaners. Decals are best applied when glass is warm (ideally greater than 50 degrees). If applied during winter months, clean glass with warm water prior to application. Place decals alone or in groups every few feet on the outside of the window. Position out of reach of infants and small children. Restore static cling by rinsing in lukewarm water. UV coating may fade based on exposure and local elevation. Replace decals every 9 to 12 months.