With the Adventure Sync feature in Pokémon GO, players can hatch Eggs and collect Candy, even when Pokémon GO is idle. Adventure Sync can record your walking distances even when Pokémon GO isn’t launched, working in the background to tally your distance, earn Candy and hatch Eggs. Adventure Sync also delivers a weekly summary, where you can see your Incubator and Candy progress as well as important activity statistics.
You can opt into Adventure Sync at any time, and the feature can connect to both Apple Health on Apple devices and Google Fit on Android devices. Due to its compatibility with the official Health app on iOS, and because it promotes walking as a means to stay active, Pokémon GO is regularly being advertised and listed within the app itself.
Source: official Pokémon GO support
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