WindowAlert decals help prevent wild birds from accidentally striking windows. Each decal features a special coating designed to reflect ultraviolet sunlight. This ultraviolet light is invisible to humans, and to the human eye the decal appears as if it were frosted or etched glass. For birds - they see a brilliant glow, much like a stoplight - which deters them from colliding with your sliding door or window. WindowAlert decals come in several designs: Butterfly, Hummingbird, Fall Medley, Snowflake, Maple Leaf, Modern Squares, Classic Squares, Pinecone, Modern Dots and Hawk. Product Specs: The static-cling modern dots decals measure approximately 1.25" across, and are designed to be placed on the exterior side of the window or glass sliding door. As a guide, the recommendation is positioning decals 4 inches horizontally and 2 inches vertically from each other. For best results, replace decals every 4 months or test with the WindowAlert UV Flashlight. What's in the box? You'll receive 1 pack of modern dots decals, with 30 decals in each pack, for a total of 30 decals.