diff --git a/CHANGELOG.md b/CHANGELOG.md
index 12ec3b3..8d043f5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   application ID or a regular expression on the window title).
 - Build tooling: `Makefile` (build/lint/pot/pack/install/nested), ESLint config,
   GitHub Actions CI, and gettext translation scaffolding (`po/`).
+- External control: writing `active-profile` from outside the extension now applies
+  that profile. Previously only the preferences process listened to the key, and only
+  to refresh its own UI, so an external writer changed nothing on screen. This makes
+  `gsettings` a supported way for another program to drive the borders without
+  duplicating the calibration.
 - `CONTRIBUTING.md` and this changelog.
 - Brazilian Portuguese translation.
 
diff --git a/README.md b/README.md
index e33232b..4be0d64 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,9 @@ for laptop users who need extra illumination without external gear.
 - **Multi-monitor support**: Show on the primary monitor or all screens.
 - **Seamless integration**: Native GNOME Shell feel with a toggle in the top bar.
 - **Convenient shortcut**: `Ctrl + Alt + L` opens the preferences.
+- **Scriptable**: apply a profile or toggle the light from any other program by
+  writing the extension's GSettings keys — see [Controlling Lighter from another
+  program](#controlling-lighter-from-another-program).
 
 ## Requirements
 
@@ -74,6 +77,51 @@ match rule — an application ID (e.g. `firefox.desktop`) and/or a window title
 matches, the optional *default profile* is applied. Manual selection always works and
 takes effect immediately.
 
+### Controlling Lighter from another program
+
+Every appearance setting lives in GSettings, and the extension reacts to external
+writes. That makes `gsettings` a supported entry point: another program can drive the
+borders without reimplementing them, and without knowing how your borders are
+calibrated.
+
+The schema is not in the default search path, so `--schemadir` is required:
+
+```bash
+SCHEMA_DIR="$HOME/.local/share/gnome-shell/extensions/lighter@gnome-shell-extensions.ferrete.com/schemas"
+SCHEMA=org.gnome.shell.extensions.lighter
+
+# Turn the light on and off
+gsettings --schemadir "$SCHEMA_DIR" set $SCHEMA enabled true
+gsettings --schemadir "$SCHEMA_DIR" set $SCHEMA enabled false
+
+# Apply a saved profile by its id
+gsettings --schemadir "$SCHEMA_DIR" set $SCHEMA active-profile '<profile-id>'
+```
+
+**Look profile ids up by name, never hardcode them.** They are UUIDs generated when
+the profile is created, so a hardcoded id breaks as soon as you recreate the profile.
+The `profiles` key holds a JSON document shaped like
+`{"version": 1, "profiles": [{"id": "…", "name": "Meet", "settings": {…}}]}`:
+
+```bash
+gsettings --schemadir "$SCHEMA_DIR" get $SCHEMA profiles \
+  | sed "s/^'//; s/'$//" \
+  | jq -r '.profiles[] | select(.name == "Meet") | .id'
+```
+
+Writing `active-profile` applies the profile, including turning the light on. The
+appearance keys (`thickness-*`, `opacity`, `color`, `temperature`, `multi-monitor`,
+`maximize-brightness`) can also be set individually and take effect immediately.
+
+Two things worth knowing:
+
+- **Turn off *Auto-switch profiles* while an external program is in charge**, or the
+  window watcher will apply its own profile on the next focus change and overwrite
+  what your program just did. The two are independent controllers of the same state.
+- **Changes to the extension's own code need a logout/login on Wayland**, because the
+  GNOME Shell cannot reload an extension there. Changes to *settings* apply
+  immediately — only code changes need the session restart.
+
 ## Development
 
 See [CONTRIBUTING.md](CONTRIBUTING.md) for the full guide. Quick start:
diff --git a/extension.js b/extension.js
index c6e6f57..7accaff 100644
--- a/extension.js
+++ b/extension.js
@@ -49,6 +49,24 @@ export default class LighterExtension extends Extension {
                 if (SYNC_KEYS.includes(key))
                     this._sync();
             });
+
+            // Applying a profile by writing `active-profile` from outside.
+            //
+            // Only the preferences process listened to this key before, and only
+            // to refresh its own UI — so an external writer could set it and
+            // nothing would happen on screen. Wiring it here makes the key a
+            // real entry point: `gsettings set ... active-profile <id>` applies
+            // the profile, which lets another program drive the borders without
+            // knowing the nine appearance keys or duplicating the calibration.
+            //
+            // No feedback loop: `applyProfile` writes `active-profile` back with
+            // the same value, and GSettings does not emit `changed` when the
+            // value is unchanged.
+            this._activeProfileId = this._settings.connect('changed::active-profile', () => {
+                const id = this._settings.get_string('active-profile');
+                if (id)
+                    this._profiles.applyProfile(id);
+            });
             this._monitorsChangedId = Main.layoutManager.connect(
                 'monitors-changed', () => this._sync());
 
@@ -73,6 +91,11 @@ export default class LighterExtension extends Extension {
             this._settingsId = 0;
         }
 
+        if (this._activeProfileId) {
+            this._settings.disconnect(this._activeProfileId);
+            this._activeProfileId = 0;
+        }
+
         if (this._monitorsChangedId) {
             Main.layoutManager.disconnect(this._monitorsChangedId);
             this._monitorsChangedId = 0;