The PokéNav, formally known as the Pokémon Navigator, is a Key Item used in Hoenn. A PokéNav is a device that stores the Hoenn map, and many other devices like the Trainers Eyes. This part of the PokéNav records all the trainers you see and meet on Pokémon Ruby, Sapphire and Emerald games and lets you check this device to see if a trainer wants a re-match. It can also record information on Elite Four trainers and the Gym Leaders and it allows them to call you for a rematch. The Pokénav also records the Pokémon ribbons you have won from contests for example "your Pelipper won a ribbon in a Normal beauty contest". Finally, it shows you how much Beauty, Cuteness, Cool etc. from when they eat PokéBlocks.
The PokéNav can be used to scan the player's Pokémon's capabilities for the Pokémon Contest. It also contains a map of the Hoenn region. In Pokémon Ruby and Sapphire, it has Trainers Eyes which the player can use to view information about certain defeated foes. In Pokémon Emerald, it has Match Call which allows the player to call other trainers.