Window Alert is a static-cling decal that may be applied to home and office windows, helping birds "see" windows and thus avoid striking the glass. 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' vision is up to 12 times better than that of humans. The Elm, Oak, and Maple leaf decals measure approximately 4" across. The two Aspen decals measure 2" across.