Percy and His Magical Items

Percy's main weapon is Anaklusmos,  the Greek word for Riptide, which is the name commonly used. It is made of celestial bronze and was given to him by Chiron. He first used it against Mrs. Dodds, his pre-algebra teacher, when she turned into a Fury and attacked him. When not in sword form, Riptide appears as a ballpoint pen that writes with celestial bronze ink, as discovered in "The House of Hades". It also always appears in his pocket when lost (though not immediately) . It will work only against gods and demigods. It passes through mortals without harming them because they are "not important enough.". It was a weapon of Heracles or Hercules , who received it from Zoë Nightshade (a child of Atlas; later became a hunter of Artemis). He also uses javelins with a grappling hook and an explosive setting on one occasion. In The Sea of Monsters, his half-brother Tyson presents him with a wristwatch that changes into a shield, but the watch is lost in The Battle of the Labyrinth.

Percy has several magical items obtained from battles against monsters. The first of these is the horn of the Minotaur, which he obtained after killing the beast. Another is the head of Medusa, which he cut off after killing it. He also obtained a lionskin coat when he killed the Nemean Lion, which he later sacrificed as an offering to Poseidon.

Source: Wikipedia