Pokemon Go Plus is the accessory to improve your Pokemon Go experience. Was originally to launch in the same month as the game, but it was disastrously pushed back to a later date. According to Niantic, that later date is September 16th.
Niantic says Pokémon GO Plus's release date will be Sept. 16.
— Takashi Mochizuki (@mochi_wsj) September 8, 2016