Literally millions of birds are injured each year flying into windows. Over the years, we have tried a number of window guards designed to reduce bird impacts. Of all models tried, this one has proven to be the most effective. The decals appear frosted (yet see-through) for humans, but are coated with a material that reflects UV light, looking like a stoplight to birds (birds see more of the light spectrum than humans). For best results, place one of these 4" diameter, static-cling decals per 3’ x 3’ section of glass. Four patterns, four decals per packet.