Years ago I sold keys and magnetic hide a key boxes. From what I remember the big hiko's seemed to have the best magnets. There may be others but try and stick it to something before you buy it. Some have very weak magnets. And the plastic boxes are better than the metal ones, the metal ones will rust shut. Don't know how long it really would take for the boxes to rust up but I have seen several so gooked up that you couldn't pry it open with a screwdriver.