Designed to prevent birds hitting windows. Although some birds will collide in the heat of a chase, most do so because they see a reflection of the sky and trees in the glass, or because there is another window or mirror in the room making the bird think there is a way through.
Double glazed windows tend to pose a greater risk than single glazed, since they produce clearer reflections. This hazard can be reduced by making the window pane more obvious to the bird. Fixing to the outside of the glass an object which will indicate that an obstacle is present should help.
There are two options available for use in different circumstances: Red Hawk silhouette, use this where the birds see see a reflection of the sky and trees in the glass. Black Hawk silhouette use this when there is another window or mirror in the room making the bird think there is a way through. Please understand that these measures will greatly reduce, but never totally solve, the problem.