When used, the Vs. Seeker sends out a signal that allows the player to find other Trainers who want a rematch. This signal affects all Trainers that are on-screen. Once used on Trainers that can be rematched, 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 if they are battled, the player leaves the area, or the player walks 100 steps. If the player attempts to use the Vs. Seeker when it is not fully charged, the player will be told how many steps remain until it is. After the player uses the Vs. Seeker, some Trainers may have their team changed from their first battle. This is typically accompanied by a change in the Trainer's dialogue and is triggered by the player reaching a certain location, earning a certain Badge, or entering the Hall of Fame. The Vs. Seeker cannot be used in indoor locations, including forests and caves, even where previously battled Trainers are present.
Red using the Vs. Seeker on Route 25. Three Trainers wish to have a rematch, while two others decline.
Generation III
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.
Generation IV
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 the Trainer has previously not been challenged, a single red exclamation mark (!) will appear instead. If a Trainer does not want to battle, they will do nothing and no bubble will appear. In Pokémon Platinum, after the player obtains the Vs. Seeker, Trainers can be found around various Sinnoh Pokémon Centers.
Generation VIII
The indication of a rematch in Generation VIII is similar to that of Generation IV. The initial reaction is a speech bubble containing a double orange exclamation mark (!!). If the Trainer has previously not been challenged, a single red exclamation mark (!) will appear instead. If a Trainer does not want to battle, they will do nothing and no bubble will appear.
In Pokémon Adventures, the Vs. Seeker works by sensing the fighting spirit of Trainers willing to battle within a certain radius and then pointing a beam of light towards them.
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, Platinum, Brilliant Diamond, and Shining Pearl, 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.