The Bird Crash Preventer was scientifically tested by the AMERICAN BIRD CONSERVANCY and proven to be highly effective. It has their recommendation.  

Dr. Daniel Klem Jr.,* a leading authority on bird-window collisions, confirms that "that 'strings are highly effective in protecting birds from striking windows, either by visually alerting them to the window hazard or physically preventing them from hitting the unyielding surface." 

David Allen Sibley, famous illustrator and author of The Sibley Guide to Birds, employed the "string" method as well. He "eliminated collisions entirely by tacking fishing lines vertically three inches apart in front of a window." But, that's a lot of work.

The Bird Crash Preventer is a ready-to-hang curtain that makes installation quick and easy. It eliminates the time-consuming job of measuring and tacking individual lines. 

*
Daniel Klem, Jr., Ph.D., D.Sc.
Professor of Biology, and
Sarkis Acopian Professor of Ornithology and Conservation Biology
Muhlenberg College, Allentown, PA 18104-5586 USA