diff --git a/lib/solaar/dbus.py b/lib/solaar/dbus.py
index 142b5904..030e98a0 100644
--- a/lib/solaar/dbus.py
+++ b/lib/solaar/dbus.py
@@ -22,23 +22,36 @@ from typing import Callable
 
 logger = logging.getLogger(__name__)
 
+system_bus: dbus.SystemBus | None = None
+session_bus: dbus.SessionBus | None = None
+
 try:
     import dbus
 
     from dbus.mainloop.glib import DBusGMainLoop  # integration into the main GLib loop
 
     DBusGMainLoop(set_as_default=True)
-    bus = dbus.SystemBus()
-    assert bus
 
-except Exception:
-    # Either the dbus library is not available or the system dbus is not running
-    logger.warning("failed to set up dbus")
-    bus = None
+    try:
+        system_bus = dbus.SystemBus()
+    except dbus.exceptions.DBusException as e:
+        logger.warning(f"Failed to connect to system dbus: {e}")
+
+    try:
+        session_bus = dbus.SessionBus()
+    except dbus.exceptions.DBusException as e:
+        logger.warning(f"Failed to connect to session dbus: {e}")
+
+except ImportError:
+    logger.warning("dbus library not available, dbus setup failed.")
+except Exception as e:
+    logger.error(f"Unexpected error during D-Bus initialization: {e}")
 
 
 _suspend_callback = None
 _resume_callback = None
+_lock_callback = None
+_unlock_callback = None
 
 
 def _suspend_or_resume(suspend):
@@ -47,9 +60,17 @@ def _suspend_or_resume(suspend):
     if not suspend and _resume_callback:
         _resume_callback()
 
+def _lock_or_unlock(locked):
+    if locked and _lock_callback:
+        _lock_callback()
+    if not locked and _unlock_callback:
+        _unlock_callback()
+
 
 _LOGIND_PATH = "/org/freedesktop/login1"
 _LOGIND_INTERFACE = "org.freedesktop.login1.Manager"
+_SCREEN_SAVER_PATH = "/ScreenSaver"
+_SCREEN_SAVER_INTERFACE = "org.freedesktop.ScreenSaver"
 
 
 def watch_suspend_resume(
@@ -61,8 +82,8 @@ def watch_suspend_resume(
     global _resume_callback, _suspend_callback
     _suspend_callback = on_suspend_callback
     _resume_callback = on_resume_callback
-    if bus is not None and on_resume_callback is not None or on_suspend_callback is not None:
-        bus.add_signal_receiver(
+    if system_bus is not None and on_resume_callback is not None or on_suspend_callback is not None:
+        system_bus.add_signal_receiver(
             _suspend_or_resume,
             "PrepareForSleep",
             dbus_interface=_LOGIND_INTERFACE,
@@ -71,6 +92,25 @@ def watch_suspend_resume(
     logger.info("connected to system dbus, watching for suspend/resume events")
 
 
+
+def watch_screen_lock_state(
+    on_lock_callback: Callable[[], None],
+    on_unlock_callback: Callable[[], None],
+):
+    """Register callbacks for screen lock/unlock events.
+    They are called only if the session DBus is running and the Desktop environments sends events on the org.freedesktop.ScreenSaver interface."""
+    global _lock_callback, _unlock_callback
+    _lock_callback = on_lock_callback
+    _unlock_callback = on_unlock_callback
+    session_bus.add_signal_receiver(
+        _lock_or_unlock,
+        "ActiveChanged",
+        dbus_interface=_SCREEN_SAVER_INTERFACE,
+        path=_SCREEN_SAVER_PATH
+    )
+    logger.info("connected to session dbus watching for screen lock/unlock events")
+
+
 _BLUETOOTH_PATH_PREFIX = "/org/bluez/hci0/dev_"
 _BLUETOOTH_INTERFACE = "org.freedesktop.DBus.Properties"
 
@@ -81,7 +121,7 @@ def watch_bluez_connect(serial, callback=None):
     if _bluetooth_callbacks.get(serial):
         _bluetooth_callbacks.get(serial).remove()
     path = _BLUETOOTH_PATH_PREFIX + serial.replace(":", "_").upper()
-    if bus is not None and callback is not None:
-        _bluetooth_callbacks[serial] = bus.add_signal_receiver(
+    if system_bus is not None and callback is not None:
+        _bluetooth_callbacks[serial] = system_bus.add_signal_receiver(
             callback, "PropertiesChanged", path=path, dbus_interface=_BLUETOOTH_INTERFACE
         )