zmk/docs/docs/behavior/outputs.md

title	sidebar_label
Output Selection Behavior	Output Selection

Summary

The output behavior allows selecting whether keyboard output is sent to the USB or bluetooth connection when both are connected. This allows connecting a keyboard to USB for power but outputting to a different device over bluetooth.

By default, output is sent to USB when both USB and BLE are connected. Once you select a different output, it will be remembered until you change it again.

Output Command Defines

Output command defines are provided through the dt-bindings/zmk/outputs.h header, which is added at the top of the keymap file:

#include <dt-bindings/zmk/outputs.h>

This allows you to reference the actions defined in this header:

Define	Action	Alias
OUTPUT_USB_CMD	Prefer sending to USB	OUT_USB
OUTPUT_BLE_CMD	Prefer sending to the current bluetooth profile	OUT_BLE
OUTPUT_TOGGLE_CMD	Toggle between USB and BLE	OUT_TOG

Output Selection Behavior

The output selection behavior changes the preferred output on press.

Behavior Binding

• Reference: &out
• Parameter #1: Command, e.g. OUT_BLE

Example:

1. Behavior binding to prefer sending keyboard output to USB

   &out OUT_USB
   

2. Behavior binding to prefer sending keyboard output to the current bluetooth profile

   &out OUT_BLE
   

3. Behavior binding to toggle between preferring USB and BLE

   &out OUT_TOG