diff --git a/api/schema.py b/api/schema.py
index d36bf54..e884cd4 100644
--- a/api/schema.py
+++ b/api/schema.py
@@ -19,12 +19,15 @@ def is_wecker_ringing() -> bool:
     if not os.path.exists(PID_FILE):
         return False
     try:
-        pid: int
         with open(PID_FILE) as f:
             pid = int(f.read().strip())
         os.kill(pid, 0)
-        return True
-    except (ValueError, ProcessLookupError, PermissionError, OSError):
+        # Guard against PID reuse: verify the running process is actually wecker.py.
+        cmdline_path = f"/proc/{pid}/cmdline"
+        with open(cmdline_path, "rb") as f:
+            cmdline = f.read().replace(b"\0", b" ").decode()
+        return "wecker.py" in cmdline
+    except (ValueError, ProcessLookupError, PermissionError, OSError, FileNotFoundError):
         return False
 
 
diff --git a/tests/test_api.py b/tests/test_api.py
index 0950517..05eabef 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -1,4 +1,4 @@
-from unittest.mock import patch
+from unittest.mock import patch, MagicMock
 from fastapi.testclient import TestClient
 import tempfile
 import os
@@ -15,6 +15,33 @@ from api.main import app  # noqa: E402
 client = TestClient(app)
 
 
+def test_is_ringing_false_on_pid_reuse():
+    """isRinging returns False when the PID file points to a non-wecker process."""
+    from api.schema import is_wecker_ringing
+
+    fake_pid = 9999
+    with patch("api.schema.PID_FILE", "/tmp/fake_reuse.pid"), \
+         patch("api.schema.os.path.exists", return_value=True), \
+         patch("api.schema.os.kill") as mock_kill, \
+         patch("builtins.open") as mock_open:
+        mock_kill.return_value = None
+
+        pid_file_mock = MagicMock()
+        pid_file_mock.read.return_value = str(fake_pid)
+        cmdline_mock = MagicMock()
+        cmdline_mock.read.return_value = b"systemd-journald"
+
+        def open_side_effect(path, *args, **kwargs):
+            if str(path).endswith("fake_reuse.pid"):
+                return pid_file_mock
+            if str(path) == f"/proc/{fake_pid}/cmdline":
+                return cmdline_mock
+            raise FileNotFoundError(path)
+
+        mock_open.side_effect = open_side_effect
+        assert is_wecker_ringing() is False
+
+
 def test_is_ringing_returns_false_when_not_running():
     """Test that isRinging returns False when no wecker process is running."""
     headers = {"X-API-Key": "test-secret"}