The Tomahawk E40 is a squirrel one way door. One way doors work by allowing the pest to exit, but not return. This device comes with mounting wings that allow it to be attached directly over the pests entry/exit hole. This device is most effective when all other potential entry points are sealed off. Proper mounting will ensure that the hole is completely blocked off, forcing the pest through the one way door. Available in 4 different sizes.