WindowAlert Hummingbird Anti-Collision Decal - UV-Reflective Window Decal to Protect Wild Birds from Glass Collisions Each pack contains four semi-transparent hummingbird static-cling reflective decals. Choose from a range of designs to fit your home decor tastes. Save the beautiful birds you love. WindowAlert stickers act as a deterrent for wild birds from flying into glass windows and sliding doors. The specially designed reflective material in each window cling reflects ultraviolet sunlight as glowing warning sign for birds. To humans they appear as frosted or etched glass. Designed for a one-time application to exterior glass surfaces. Before application, ensure that your surface is thoroughly clean and free of any overlay, tinting, film, coating or other impurities. WindowAlert is the trusted source for prevention of bird window strikes and window collisions. WindowAlert first developed and pioneered ultraviolet window decals in Bend, Oregon in 2003. Decals are made in the USA.