I was wondering if someone can find a statement on what counts your walking distance when using Pokémon Go Plus. Does it use the phone or the Pokémon Go Plus instead? All articles I can find only state that it is counted, but not how it is done.
This article mentions how the Pokemon Go Plus accessory tracks your distance walked:
This is a key part of the product, as the Plus uses your phone’s capabilities to leave GPS running in the background, much like you see with navigation apps that are actively guiding you during trips.
Thus, if you are only wearing the Pokemon Go Plus accessory and do not have your phone with you, your distance walked will not be tracked.
It uses GPS of the phone to count the distance. I read somewhere that it takes snapshot of coordinates every 15 seconds and measures distance between those 2 points. So if you take a lot of turns, it can measure shorter distance than you walked.