When used, the Vs. Seeker sends out a signal that allows Pokémon Trainers to find other Trainers who want a rematch. This signal affects all Trainers that are within the player's view. Once used, the device cannot be used again until it is charged. The player does this by walking a total of 100 steps. The effect on the Trainers wears off either when they have been battled, when the player leaves the route, or when the player walks 100 steps within the route. If the player attempts to use the Vs. Seeker when it is not fully charged, the player will be told how many steps remain for it to function. It should be noted that after using the Vs. Seeker, some Trainers may have higher-leveled Pokémon than the last battle, and their Pokémon may even have evolved. This usually happens when certain events relative to the opponent trainer's location have happened, such as the player beating the region's Gym Leader, but can also happen if events in far-away locations have been triggered, such as beating the Elite Four. The Vs. Seeker is also unable to be used in buildings or caves, even where previously battled Trainers are present.
Red uses the Vs. Seeker on Route 25. Three Trainers wish to have a rematch, while two others decline.
The indication of a rematch is initially a speech bubble above the Trainers' heads with a black double exclamation mark (!!). After that, the Trainers jump up and down or raise their hands to remind the player post-battle of who wanted a re-match. Trainers that have not been battled previously by the player display a single red exclamation mark (!), and do not jump up and down. Trainers that do not wish to battle do not do anything and display a blue bubble containing a white X.
The indication of a rematch in Generation IV is similar to that of Generation III. The initial reaction is a speech bubble containing a double red exclamation mark (!!), and the Trainers rotate in place afterwards. If a Trainer does not want to battle, they will do nothing.
In the official artwork, as well as their in-game sprites and Super Smash Bros. Ultimate models, Red's Vs. Seeker is blue and Leaf's is pink. However, standalone artwork depicts it as blue by default, and the in-game bag sprite is blue even when playing as Leaf.
The PokéNav and the Vs. Seeker resemble each other somewhat in appearance, and both serve the purpose of allowing players to rechallenge Trainers they previously battled.
Using the Vs. Seeker does not temporarily lower the volume of any current background music, such as Cynthia's theme, when playing the Piano in the Villa of Pokémon Platinum.
In Diamond, Pearl, and Platinum, if the player uses the Vs. Seeker on a certain area of the cycling road part of Route 206, it is possible to catch the attention of a Hiker below the road. However, it is impossible to fight him without using the Vs. Seeker again, as there is a gate on the way.
While not used, the Vs. Seeker bag sprite appears in the coding for Generation V games, along with all other items seen only in Generation III and IV.