The Poke Radar is received from Professor Rowan after you have completed the Sinnoh Pokedex in "Pokemon Platinum." The Poke Radar can be used in normal grass to indicate where Pokemon can be encountered. If the grass ruffles violently there is a chance that a rare Pokemon is there. A sparkle in the grass indicates that a shiny Pokemon is in that patch of grass. Walk to the reactive tile of grass to trigger a battle with the Pokemon that caused the rustle.
Instructions
1
See all 210 Pokemon in the Sinnoh Pokedex.
2
Go to Sangdem Town and talk to Professor Rowan.
3
Obtain the Poke Radar from Professor Rowan after you receive the National Pokedex.