diff --git a/enodia_sentinel/tray/notify.py b/enodia_sentinel/tray/notify.py
new file mode 100644
index 0000000..45706df
--- /dev/null
+++ b/enodia_sentinel/tray/notify.py
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""Desktop notification helper. Prefers notify-send; no GUI imports."""
+from __future__ import annotations
+
+import shutil
+import subprocess
+from typing import Callable, Optional, Sequence
+
+Runner = Callable[[Sequence[str]], "subprocess.CompletedProcess"]
+
+
+def _default_runner(cmd: Sequence[str]) -> "subprocess.CompletedProcess":
+    try:
+        return subprocess.run(list(cmd), capture_output=True, text=True,
+                              timeout=10, check=False)
+    except (OSError, subprocess.TimeoutExpired) as exc:
+        return subprocess.CompletedProcess(list(cmd), 127, "", str(exc))
+
+
+def notify(title: str, body: str, *, runner: Optional[Runner] = None,
+           which: Callable[[str], object] = shutil.which) -> bool:
+    """Show a desktop notification. Returns True if notify-send was invoked."""
+    if which("notify-send") is None:
+        return False
+    run = runner or _default_runner
+    run(["notify-send", "-a", "Enodia Sentinel", title, body])
+    return True
diff --git a/tests/test_tray_notify.py b/tests/test_tray_notify.py
new file mode 100644
index 0000000..f55caf3
--- /dev/null
+++ b/tests/test_tray_notify.py
@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""Desktop notification helper: notify-send when available, else no-op."""
+import subprocess
+import unittest
+
+from enodia_sentinel.tray import notify
+
+
+class TestNotify(unittest.TestCase):
+    def test_no_notify_send_is_noop(self):
+        calls = []
+
+        def runner(cmd):
+            calls.append(cmd)
+            return subprocess.CompletedProcess(cmd, 0)
+
+        used = notify.notify("t", "b", runner=runner, which=lambda _n: None)
+        self.assertFalse(used)
+        self.assertEqual(calls, [])
+
+    def test_uses_notify_send_with_app_name(self):
+        calls = []
+
+        def runner(cmd):
+            calls.append(cmd)
+            return subprocess.CompletedProcess(cmd, 0)
+
+        used = notify.notify("Title", "Body", runner=runner,
+                             which=lambda _n: "/usr/bin/notify-send")
+        self.assertTrue(used)
+        self.assertEqual(len(calls), 1)
+        self.assertIn("notify-send", calls[0][0])
+        self.assertIn("Title", calls[0])
+        self.assertIn("Body", calls[0])