diff --git a/pkgs/applications/misc/psi-notify/default.nix b/pkgs/applications/misc/psi-notify/default.nix
new file mode 100644
index 00000000000..5a4b6f385df
--- /dev/null
+++ b/pkgs/applications/misc/psi-notify/default.nix
@@ -0,0 +1,39 @@
+{ lib, stdenv, fetchFromGitHub, systemd, libnotify, pkg-config }:
+
+stdenv.mkDerivation rec {
+  pname = "psi-notify";
+  version = "1.2.1";
+
+  src = fetchFromGitHub {
+    owner = "cdown";
+    repo = pname;
+    rev = version;
+    sha256 = "0hn37plim1smmlrjjmz8kybyms8pz3wxcgf8vmqjrsqi6bfcym7g";
+  };
+
+  buildInputs = [ systemd libnotify ];
+  nativeBuildInputs = [ pkg-config ];
+
+  installPhase = ''
+    runHook preInstall
+
+    install -D psi-notify $out/bin/psi-notify
+    substituteInPlace psi-notify.service --replace psi-notify $out/bin/psi-notify
+    install -D psi-notify.service $out/share/systemd/user/psi-notify.service
+
+    runHook postInstall
+  '';
+
+  meta = with lib; {
+    description = "Alert on system resource saturation";
+    longDescription = ''
+      psi-notify can alert you when resources on your machine are becoming
+      oversaturated, and allow you to take action before your system slows to a
+      crawl.
+    '';
+    license = licenses.mit;
+    homepage = "https://github.com/cdown/psi-notify";
+    platforms = platforms.linux;
+    maintainers = with maintainers; [ eduarrrd ];
+  };
+}
diff --git a/pkgs/tools/audio/playerctl/default.nix b/pkgs/tools/audio/playerctl/default.nix
index 15ebb93e4e8..d9f408bf9ed 100644
--- a/pkgs/tools/audio/playerctl/default.nix
+++ b/pkgs/tools/audio/playerctl/default.nix
@@ -2,13 +2,13 @@
 
 stdenv.mkDerivation rec {
   pname = "playerctl";
-  version = "2.3.1";
+  version = "2.4.1";
 
   src = fetchFromGitHub {
     owner = "acrisci";
     repo = "playerctl";
     rev = "v${version}";
-    sha256 = "00z5c6amlxd3q42l7x8i0ngl627dxglgg5vikbbhjp9ms34xbxdn";
+    sha256 = "sha256-OiGKUnsKX0ihDRceZoNkcZcEAnz17h2j2QUOSVcxQEY=";
   };
 
   nativeBuildInputs = [ meson ninja pkg-config gtk-doc docbook_xsl gobject-introspection ];
diff --git a/pkgs/tools/nix/nix-output-monitor/default.nix b/pkgs/tools/nix/nix-output-monitor/default.nix
index 94c5f0afb2c..a94ae45ccea 100644
--- a/pkgs/tools/nix/nix-output-monitor/default.nix
+++ b/pkgs/tools/nix/nix-output-monitor/default.nix
@@ -5,11 +5,11 @@
 }:
 mkDerivation rec {
   pname = "nix-output-monitor";
-  version = "1.0.3.2";
+  version = "1.0.3.3";
   src = fetchFromGitHub {
     owner = "maralorn";
     repo = "nix-output-monitor";
-    sha256 = "0srfclmqrqcx8b756yxww24ya0xn2ajxbgj07mcvdvwbwl09pys8";
+    sha256 = "1x26s9gzcygn96600g0r1a1sxqav6c38iq981rhmc808mqlyxmp8";
     rev = "v${version}";
   };
   isLibrary = true;
diff --git a/pkgs/tools/package-management/nix/default.nix b/pkgs/tools/package-management/nix/default.nix
index ad2fe6bb97b..a5fb98d7557 100644
--- a/pkgs/tools/package-management/nix/default.nix
+++ b/pkgs/tools/package-management/nix/default.nix
@@ -228,13 +228,13 @@ in rec {
   nixUnstable = lib.lowPrio (callPackage common rec {
     pname = "nix";
     version = "2.4${suffix}";
-    suffix = "pre20210908_${lib.substring 0 7 src.rev}";
+    suffix = "pre20210922_${lib.substring 0 7 src.rev}";
 
     src = fetchFromGitHub {
       owner = "NixOS";
       repo = "nix";
-      rev = "3c56f62093601143838af923195f630d8ffae2d4";
-      sha256 = "sha256-pjdzLOEt8i1NQe4drLpp8+LrRd2MgsISSQEsMebz2kc=";
+      rev = "bcd73ebf60bb9ba6cb09f8df4366d5474c16e4a4";
+      sha256 = "sha256-wRbz8c22tlRn2/va/yOoLJijdJn+JJqLRDPRlifaEEA=";
     };
 
     boehmgc = boehmgc_nixUnstable;
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 94dc6acf06a..941dbd125f4 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -25437,6 +25437,8 @@ in
   prevo-data = callPackage ../applications/misc/prevo/data.nix { };
   prevo-tools = callPackage ../applications/misc/prevo/tools.nix { };
 
+  psi-notify = callPackage ../applications/misc/psi-notify { };
+
   ptex = callPackage ../development/libraries/ptex {};
 
   pyright = nodePackages.pyright;