In the Pokémon TV series, the device used to identify and record Pokémon is the Pokédex.
Professor Oak gives Ash a Pokédex at the beginning of his journey. The electronic encyclopedia identifies Pokémon and provides information about species Ash encounters, helping him learn about the creatures he hopes to find and study.
The Pokédex is a recurring symbol of the Pokémon world’s scientific approach to exploration. Different regions use updated models, so its appearance and voice can change across series, while its basic purpose remains the same.
The PokéNav and Pokégear are different devices from the Pokémon games and related stories. They provide navigation, communication, or mapping features, whereas the Pokédex is specifically associated with cataloguing Pokémon species.