zmk-switch-layer

ZMK module to persistently switch layers. There is no need for a physical switch and no need to flash again (for example like the logitech keyboards that activate the macos and windows layer), the change always remains active, after reboot, after flash and after power off. The keyboard can toggle the base layer other any layer while using the keyboard.

It includes two independent behaviors:

• switch-layer-mode: activates an alternative layer above another without changing the default layer
• switch-default-layer-mode: changes the persistent default layer between two options

Features

Feature	Support	Note
Keeps the mode after power off or reboot	Yes	Uses ZMK settings: zmk_switch_layer/mode.
Changes the persistent default layer	No	Does not call zmk_keymap_layer_to().
Activates one layer above another	Yes	Activates target-layer when source-layer is active and the stored mode is target.
Restores when leaving source-layer	Yes	Deactivates target-layer if it was activated by this module.
Allows returning manually to normal mode	Yes	Use &sw_layer 0.
Allows toggling from one key	Yes	Use &sw_layer 2.
Requires layers to be base or layer 0	No	They can be any pair of layers from the keymap.
Can activate a layer that is also base/default	Yes	Activates it as a normal layer; does not store it as default.
Multiple layer pairs	Partial	Multiple nodes can be defined, but they share the same global persistent mode.

Add As External Module

Add it to west.yml:

CONFIG_SETTINGS must be enabled.

manifest:
  remotes:
    - name: mctechnology17
      url-base: https://github.com/mctechnology17
  projects:
    - name: zmk-switch-layer
      remote: mctechnology17
      revision: main
  self:
    path: config

Compatible:

zmk-switch-layer,behavior-switch-layer-mode
zmk-switch-layer,behavior-switch-default-layer-mode

Kconfig:

CONFIG_ZMK_SWITCH_LAYER_BEHAVIOR
CONFIG_ZMK_SWITCH_DEFAULT_LAYER_BEHAVIOR

Local build:

-DZMK_EXTRA_MODULES="/path/to/zmk-switch-layer"

switch-default-layer-mode

switch-default-layer-mode changes the default layer and keeps the mode after power off or reboot.

Example:

/ {
    behaviors {
        /omit-if-no-ref/ sw_default: switch_default_layer_mode {
            compatible = "zmk-switch-layer,behavior-switch-default-layer-mode";
            #binding-cells = <1>; /* 0: source, 1: target, 2: toggle */
            source-layer = <_DEFAULT>;
            target-layer = <_WINDOWS>;
        };
    };
};

Usage:

&sw_default 1  /* use target-layer as default */
&sw_default 0  /* return to source-layer as default */
&sw_default 2  /* toggle */

switch-layer-mode

Define the behavior in the keymap:

/ {
    behaviors {
        /omit-if-no-ref/ sw_layer: switch_layer_mode {
            compatible = "zmk-switch-layer,behavior-switch-layer-mode";
            #binding-cells = <1>; /* 0: source, 1: target, 2: toggle */
            source-layer = <_SYMBOL>;
            target-layer = <_LINUX>;
        };
    };
};

Add control keys:

&sw_layer 1  /* use target-layer when source-layer is active */
&sw_layer 0  /* return to source-layer */
&sw_layer 2  /* toggle */

Multiple switch-layer-mode

The behavior is not limited to one layer or one pair. You can define multiple nodes with the same compatible and change the source-layer / target-layer pair in each one:

/ {
    behaviors {
        sw_symbol_linux: switch_symbol_linux {
            compatible = "zmk-switch-layer,behavior-switch-layer-mode";
            #binding-cells = <1>;
            source-layer = <_SYMBOL>;
            target-layer = <_LINUX>;
        };

        sw_nav_game: switch_nav_game {
            compatible = "zmk-switch-layer,behavior-switch-layer-mode";
            #binding-cells = <1>;
            source-layer = <_NAV>;
            target-layer = <_GAME>;
        };
    };
};

Usage:

&sw_symbol_linux 2
&sw_nav_game 2

Related Topics and short comparison

Module / feature	What it does	Persistent	Changes default layer
switch-layer-mode	When source-layer is active, decides whether to mount target-layer above it according to a stored mode.	Yes	No
switch-default-layer-mode	Changes the default layer between source-layer and target-layer according to a stored mode.	Yes	Yes
zmk-auto-layer	Activates a temporary layer and keeps it active while keys allowed by a continue-list are pressed.	No	No
elpekenin's default-layer	Changes the default layer and stores it.	Yes	Yes
ZMK layer behaviors	&mo, &tog, &to and layer-tap activate, toggle or change layers from a key.	No	&to can change the active base layer at runtime, but does not store it
ZMK conditional layers	Activates a layer when a set of other layers is already active.	No	No
ZMK persistent settings	Infrastructure for storing state in flash. Not a layer behavior by itself.	Yes	No

Credit

This module is based on elpekenin/zmk-userspace and his great work on persistent ZMK behaviors.

This implementation is separated as zmk-switch-layer, with its own compatible, Kconfig, settings and sources.

Difference from elpekenin's default-layer behavior

elpekenin's default-layer behavior changes the persistent default layer.

switch-layer-mode does not change the default layer. It stores a persistent mode and, when source-layer is active, decides whether target-layer should also be activated above it.

switch-default-layer-mode does change the persistent default layer, but it stays separate so it can be used or removed without affecting switch-layer-mode.