Keys of Hades

The Keys of Hades are magic "keys" owned by Hades. They have the power to "seal" or "free" people in The Underworld, which means someone could bring someone from or send someone to the Underworld or Tartarus with the keys.

The Demigod Files
====Percy Jackson and the Sword of Hades One of these keys were placed inside the Sword of Hades. It is said that one touch of the sword on someone's body can send it's soul to the Underworld or release it's soul from the Underworld. The sword had been stolen and what Persephone feared was that anyone in possession with it could release anyone from the Underworld (as the sword possessed a key of Hades which had such power). Percy thought that Hades was a deceitful god for forging the sword, but it turned out that he didn't know that it was made. He knew it would upset the power balance between the Big Three, and he was angry with Persephone for going behind his back and having it made.