diff --git a/flake.lock b/flake.lock
index 67d7bb3..993cff1 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,5 +1,21 @@
 {
   "nodes": {
+    "dark-mode-notify-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1657531789,
+        "narHash": "sha256-m/VTRz0lu+BMETRVY+6tESDNhKwlpNwfwMZ45BMwYzk=",
+        "owner": "bouk",
+        "repo": "dark-mode-notify",
+        "rev": "5ac81063f442ea72dab457c777d1860754cfaede",
+        "type": "github"
+      },
+      "original": {
+        "owner": "bouk",
+        "repo": "dark-mode-notify",
+        "type": "github"
+      }
+    },
     "darwin": {
       "inputs": {
         "nixpkgs": [
@@ -123,6 +139,7 @@
     },
     "root": {
       "inputs": {
+        "dark-mode-notify-src": "dark-mode-notify-src",
         "darwin": "darwin",
         "flake-compat": "flake-compat",
         "flake-utils": "flake-utils",
diff --git a/flake.nix b/flake.nix
index 00f1d3c..bb3b99e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -16,6 +16,11 @@
     # Other sources
     flake-compat = { url = github:edolstra/flake-compat; flake = false; };
     flake-utils.url = github:numtide/flake-utils;
+
+    dark-mode-notify-src = {
+      url = github:bouk/dark-mode-notify;
+      flake = false;
+    };
   };
 
   outputs = { self, darwin, nixpkgs, home-manager, flake-utils, ... }@inputs:
@@ -28,12 +33,17 @@
       nixpkgsConfig = {
         config = { allowUnfree = true; };
         overlays = attrValues self.overlays ++ singleton (
-          final: prev: optionalAttrs
-            (prev.stdenv.system == "aarch64-darwin")
+          final: prev:
             {
-              # Sub in x86 version of packages that don't build on Apple Silicon yet
-              inherit (final.pkgs-x86);
-            } // final.patched
+              dark-mode-notify = final.callPackage ./pkgs/dark-mode-notify.nix { inherit (inputs) dark-mode-notify-src; };
+            } // optionalAttrs
+              (prev.stdenv.system == "aarch64-darwin")
+              {
+                # Sub in x86 version of packages that don't build on Apple Silicon yet
+                inherit (final.pkgs-x86);
+                # Sub in one off patches
+                inherit (final.patched);
+              }
         );
       };
 
diff --git a/home/shells.nix b/home/shells.nix
index 4060fe7..c0d1de9 100644
--- a/home/shells.nix
+++ b/home/shells.nix
@@ -6,7 +6,9 @@
   programs.fish.enable = true;
 
   # Add Fish plugins
-  home.packages = with pkgs.fishPlugins; [ done ];
+  home.packages = with pkgs.fishPlugins; [
+    done
+  ];
 
   programs.fish.plugins = [
     {
@@ -68,16 +70,26 @@
     # Set `$term_background` based on whether macOS is light or dark mode. Other Fish functions
     # trigger when this variable changes. We use a universal variable so that all instances of Fish
     # have the same value for the variable.
-    set-background-to-macOS = {
+    set-background-to-macOS.body = ''
+      # Returns 'Dark' if in dark mode fails otherwise.
+      if defaults read -g AppleInterfaceStyle &>/dev/null
+        set -U term_background dark
+      else
+        set -U term_background light
+      end
+    '';
+
+    # Set `$term_background` based on an env var.
+    set-background-to-env = {
+      argumentNames = [ "env_var" ];
       body = ''
-        # Returns 'Dark' if in dark mode fails otherwise.
-        if defaults read -g AppleInterfaceStyle &>/dev/null
+        switch $$env_var
+        case 1
           set -U term_background dark
-        else
+        case 0
           set -U term_background light
         end
       '';
-      onVariable = "PWD";
     };
 
     # Sets Fish Shell to light or dark colorscheme based on `$term_background`.
@@ -211,4 +223,24 @@
     # username.style_user = "bold blue"; # don't like the default
   };
   # }}}
+
+  # dark-mode-notify configuration
+  # {{{
+  launchd.enable = true;
+  launchd.agents.dark-mode-notify = {
+    enable = true;
+    config = {
+      Label = "ke.bou.dark-mode-notify";
+      KeepAlive = true;
+      StandardErrorPath = null;
+      StandardOutPath = null;
+      ProgramArguments = [
+        "${pkgs.dark-mode-notify}/bin/dark-mode-notify"
+        "${pkgs.fish}/bin/fish"
+        "-c"
+        "set-background-to-env DARKMODE"
+      ];
+    };
+  };
+  # }}}
 }
diff --git a/pkgs/dark-mode-notify.nix b/pkgs/dark-mode-notify.nix
new file mode 100644
index 0000000..bf74da8
--- /dev/null
+++ b/pkgs/dark-mode-notify.nix
@@ -0,0 +1,26 @@
+{ stdenv
+, lib
+, xcodeenv
+, dark-mode-notify-src
+, ...
+}:
+let
+  sdkVersion = "13.4.1";
+  xcode = xcodeenv.composeXcodeWrapper {
+    version = sdkVersion;
+    xcodeBaseDir = "/Applications/Xcode.app";
+  };
+in
+stdenv.mkDerivation {
+  name = "dark-mode-notify";
+  src = dark-mode-notify-src;
+  buildPhase = ''
+    ${xcode}/bin/xcrun swiftc dark-mode-notify.swift -o dark-mode-notify
+  '';
+  installPhase = ''
+    mkdir -p $out/bin
+    cp dark-mode-notify $out/bin
+  '';
+  meta.platforms = lib.platforms.darwin;
+}
+