Each year millions of wild birds are killed flying into home windows or office windows. They may see plants on the window sill and think it is outside, or simply cannot see the clean glass. Window-Alert static cling decals reflect the sunlight so, while we don't see anything from indoors, to a bird it will look like a maple leaf, a butterfly or a hawk and it works like a stop light. Birds have vision up to 12 times better than humans. Save the birds and yourself the sadness of seeing a beautiful bird laying dead in the yard with a broken neck!
My friend at Cornell Lab of Ornithology has suggested some additonal ways to keep birds from hurting themselves. Most of these are much more expensive than the window decals, but you should know they exist and you may want to try them. The link to this information is on the links page as Cornell Lab #3e.
