Unfortunately, the University of Nebraska (who did the original studies on the efficacy of lines and a hoop device as they affect birds) did not officially endorse the Magic Halo for use in this application. You can read that study paper HERE (pdf).
Therefore, we cannot guarantee positive results in nest box applications. Despite that, our "test customer" is having wonderful success using the halo, having tried a "sparrow spooker" first without luck.
Stay tuned for more result updates as we learn of them!