How is a clear plastic bag of water, above the door, a good way to keep flys (insects) out of the house?

Actually, the way to keep flys away is a clear plastic bag, filled half way with water, and a few old (pre-1980) pennies inside.





The copper in the pennies reacts with the water and releases negative ions, which the flys somehow detect, and it keeps them away.





When you cremate someone, the urns are made of copper for the same reason. Copper reacts with the environment and keeps bugs away.How is a clear plastic bag of water, above the door, a good way to keep flys (insects) out of the house?
~~The bag needs to be half full of water, and needs to only hang above the door itself. Actually 2 bags work even better. It disorients them and they turn around and leave. I can only tell you it works on flies, I'm not sure about any other insect.~~How is a clear plastic bag of water, above the door, a good way to keep flys (insects) out of the house?
I've been told that the water bag screws up the flys eyesight and they wont go in that direction.