Today during Nintendo's E3 presentation, Shigeru Miyamoto revealed Nintendo hopes to have the Pokémon GO Plus device ready by the end of July, at a cost of $34.99.
Pokemon GO Plus will flash green and vibrate to alert you when a Pokémon is nearby, freeing you from needing to monitor your phone while walking.You can also throw a Pokéball just using this device. The flashing light also changes to a rainbow pattern if a Pokémon is successfully caught, and red when it fails.
During the live stream was mentioned that the Pokémon GO app will be available for download at no charge on the App Store and Google Play, and it would need to be ready before the device, putting the official release for Pokémon GO sometime next month.
Get ready to cath 'em all!
Source: Pokémon Co. /Nintendo @E3