I don’t really know how these work. I’m assuming they are supposed to be powerful enough to magnetize through a door. They are not. But beware they WILL magnetize through your finger while you are trying to get them situated. I had to get my husband to pull them off. Lost a nail and smashed my finger. Get a command strip. I still haven’t grown the nail out. 

Also the hooks bend off easily and break. Learned that trying to detach them from my hand.