Prominent wizard families have their Wills protected by magic. This means their homes are sealed and can only be opened by the beneficiary, to ensure their wishes are carried out. The Potters’ will specified that only their children could open the door. Harry can’t even do it. They all think it’s lost to the world now, but as Sirius mournfully places his hand on the door to say goodbye to the Potter home, it opens. He cries for hours in front of a painting of Fleamont and Euphemia. He’s home.