qmk-firmware/docs/feature_bluetooth.md

Bluetooth

Bluetooth Functionality

This requires some hardware changes, but can be enabled via the Makefile. The firmware will still output characters via USB, so be aware of this when charging via a computer. It would make sense to have a switch on the Bluefruit to turn it off at will.

Bluetooth Keycodes

This is used when multiple keyboard outputs can be selected. Currently this only allows for switching between USB and Bluetooth on keyboards that support both.

Name	Description
OUT_AUTO	Automatically switch between USB and Bluetooth
OUT_USB	USB only
OUT_BT	Bluetooth only