The PokéRadar is one of the most important items a player can obtain in Pokémon Brilliant Diamond and Brilliant Pearl. This Pokétch device app will be extremely useful when it comes to tracking Shiny Pokémon.
To get the PokéRadar, players will need to put some effort into it first. You must unlock the National PokéDex before you can get it. The good news is that this doesn't mean you have to catch all the Pokémon in the game, you just have to meet them. This will save you a lot of time on your mission.
Once the PokéDex is complete, head to Sandgem Town and talk to Professor Rowan. Show him the PokéDex and Professor Oak will come and talk about the National Dex. Next, head to Ramanas Park and you'll find Professor Oak again and he'll give you the PokéRadar upgrade for your Pokétch.
If you are concerned about adding Palkia or Dialga to your PokéDex, depending on the version you purchased. All you have to do is beat the Elite Four, then go to Celestic Town. Enter the house near the celestial ruins and you will find an NPC who tells you everything about Mount Coronet. This will actually add the Pokémon you are missing to your Dex.