diff --git a/focus_time_app/cli/commands/configuration_command.py b/focus_time_app/cli/commands/configuration_command.py
index eca3591..b004519 100644
--- a/focus_time_app/cli/commands/configuration_command.py
+++ b/focus_time_app/cli/commands/configuration_command.py
@@ -15,6 +15,7 @@
 from focus_time_app.focus_time_calendar.adapter_factory import create_calendar_adapter
 from focus_time_app.focus_time_calendar.event import CalendarType
 from focus_time_app.utils import is_production_environment
+from focus_time_app.utils.os_notification import OsNativeNotificationImpl
 
 
 class ConfigurationCommand:
@@ -53,7 +54,8 @@ def run(self):
         configuration = ConfigurationV1(calendar_type=calendar_type, calendar_look_ahead_hours=0,
                                         calendar_look_back_hours=0, focustime_event_name="Foo", start_commands=[],
                                         stop_commands=[], dnd_profile_name="foo",
-                                        set_event_reminder=False, event_reminder_time_minutes=0)
+                                        set_event_reminder=False, event_reminder_time_minutes=0,
+                                        show_notification=False)
         calendar_adapter = create_calendar_adapter(configuration)
         while True:
             adapter_configuration = calendar_adapter.authenticate()
@@ -74,6 +76,8 @@ def run(self):
 
         self._configure_event_reminders(configuration)
 
+        self._configure_notification(configuration)
+
         if not self._skip_install_dnd_helper:
             CommandExecutorImpl.install_dnd_helpers()
 
@@ -158,3 +162,16 @@ def _configure_event_reminders(configuration: ConfigurationV1):
                                  "reminder be shown?", type=int, default=15, prompt_suffix='\n')
                 if configuration.event_reminder_time_minutes > 0:
                     break
+
+    @staticmethod
+    def _configure_notification(configuration: ConfigurationV1):
+        prompt_message = "Do you want the Focus Time app to show a system notification whenever a focus time " \
+                         "starts or stops? If you choose yes, a test notification will be shown."
+        if sys.platform == "darwin":
+            prompt_message += " If you configure this app for the first time, macOS will request from you to allow " \
+                              "notifications (see top right corner of your screen)."
+
+        configuration.show_notification = typer.confirm(prompt_message, default=True, prompt_suffix='\n')
+
+        if configuration.show_notification:
+            OsNativeNotificationImpl.send_notification("Focus Time App test", "This is a dummy notification")
diff --git a/focus_time_app/cli/commands/sync_command.py b/focus_time_app/cli/commands/sync_command.py
index a602421..fc5b315 100644
--- a/focus_time_app/cli/commands/sync_command.py
+++ b/focus_time_app/cli/commands/sync_command.py
@@ -1,4 +1,7 @@
 import logging
+import time
+from _zoneinfo import ZoneInfo
+from datetime import datetime
 
 import typer
 
@@ -8,6 +11,10 @@
 from focus_time_app.focus_time_calendar.abstract_calendar_adapter import AbstractCalendarAdapter
 from focus_time_app.focus_time_calendar.event import FocusTimeEvent
 from focus_time_app.focus_time_calendar.utils import get_active_focustime_event
+from focus_time_app.utils import human_readable_timedelta
+from focus_time_app.utils.os_notification import OsNativeNotificationImpl
+
+NOTIFICATION_TIME_FORMAT = "%H:%M"
 
 
 class SyncCommand:
@@ -20,13 +27,21 @@ def run(self):
         events = self._calendar_adapter.get_events()
         self._adjust_reminder_time_if_necessary(events)
         marker_file_exists = Persistence.ongoing_focustime_markerfile_exists()
-        if get_active_focustime_event(events):
+        if active_focustime := get_active_focustime_event(events):
             if marker_file_exists:
                 msg = "Focus time is already active. Exiting ..."
                 typer.echo(msg)
                 self._logger.info(msg)
             else:
-                msg = "Found a new focus time, calling start command(s) ..."
+                if self._configuration.show_notification:
+                    title = "Focus time starts now"
+                    remaining_minutes = human_readable_timedelta(active_focustime.end - datetime.now(ZoneInfo('UTC')))
+                    message = f"Time remaining: {remaining_minutes} " \
+                              f"(until {active_focustime.end.astimezone().strftime(NOTIFICATION_TIME_FORMAT)})"
+                    OsNativeNotificationImpl.send_notification(title, message)
+
+                msg = f"Found a new focus time (from {active_focustime.start} to {active_focustime.end}), " \
+                      f"calling start command(s) ..."
                 typer.echo(msg)
                 self._logger.info(msg)
                 try:
@@ -37,12 +52,17 @@ def run(self):
 
         else:
             if marker_file_exists:
-                msg = "No focus time is active, calling stop command(s) ..."
+                msg = "No focus time is active anymore, calling stop command(s) ..."
                 typer.echo(msg)
                 self._logger.info(msg)
                 try:
                     CommandExecutorImpl.execute_commands(self._configuration.stop_commands,
                                                          self._configuration.dnd_profile_name)
+
+                    if self._configuration.show_notification:
+                        title = "Focus time has ended"
+                        message = "Your configured stop-commands have been called"
+                        OsNativeNotificationImpl.send_notification(title, message)
                 finally:
                     Persistence.set_ongoing_focustime(ongoing=False)
             else:
diff --git a/focus_time_app/configuration/configuration.py b/focus_time_app/configuration/configuration.py
index 203212c..7c0bae5 100644
--- a/focus_time_app/configuration/configuration.py
+++ b/focus_time_app/configuration/configuration.py
@@ -34,8 +34,9 @@ class ConfigurationV1:
     dnd_profile_name: str = field(metadata={"validate": marshmallow.validate.Length(min=1)})
     set_event_reminder: bool
     event_reminder_time_minutes: int = field(metadata={"validate": marshmallow.validate.Range(min=0)})
-    version: int = field(default=1)
+    show_notification: bool = field(default=False)
     adapter_configuration: Optional[Dict[str, Any]] = field(default=None)
+    version: int = field(default=1)
 
 
 ConfigurationV1Schema = marshmallow_dataclass.class_schema(ConfigurationV1)
diff --git a/focus_time_app/utils/__init__.py b/focus_time_app/utils/__init__.py
index 4af8211..1b1712e 100644
--- a/focus_time_app/utils/__init__.py
+++ b/focus_time_app/utils/__init__.py
@@ -1,4 +1,5 @@
 import sys
+from datetime import timedelta
 from os import getenv
 
 # keep the values in sync with env vars set in the CI/CD YAML (workflow) files
@@ -23,3 +24,19 @@ def get_environment_suffix() -> str:
     if is_production_environment():
         return ""
     return "-dev"
+
+
+def human_readable_timedelta(duration: timedelta) -> str:
+    data = {}
+    data['days'], remaining = divmod(duration.total_seconds(), 86_400)
+    data['hours'], remaining = divmod(remaining, 3_600)
+    data['minutes'], data['seconds'] = divmod(remaining, 60)
+
+    del data['seconds']  # we do not need this degree of precision
+
+    time_parts = ((name, round(value)) for name, value in data.items())
+    time_parts = [f'{value} {name[:-1] if value == 1 else name}' for name, value in time_parts if value > 0]
+    if time_parts:
+        return ' '.join(time_parts)
+    else:
+        return 'below 1 second'
diff --git a/focus_time_app/utils/os_notification/__init__.py b/focus_time_app/utils/os_notification/__init__.py
new file mode 100644
index 0000000..84c9b58
--- /dev/null
+++ b/focus_time_app/utils/os_notification/__init__.py
@@ -0,0 +1,17 @@
+import sys
+from typing import Optional
+
+from focus_time_app.utils.os_notification.abstract_os_notification import AbstractOsNotification
+
+OsNativeNotificationImpl: Optional[AbstractOsNotification] = None
+
+if sys.platform == "win32":
+    from focus_time_app.utils.os_notification.win_os_notification import WinOsNotification
+
+    OsNativeNotificationImpl = WinOsNotification()
+elif sys.platform == "darwin":
+    from focus_time_app.utils.os_notification.macos_os_notification import MacosOsNotification
+
+    OsNativeNotificationImpl = MacosOsNotification()
+else:
+    raise NotImplementedError
diff --git a/focus_time_app/utils/os_notification/abstract_os_notification.py b/focus_time_app/utils/os_notification/abstract_os_notification.py
new file mode 100644
index 0000000..e8f9a6e
--- /dev/null
+++ b/focus_time_app/utils/os_notification/abstract_os_notification.py
@@ -0,0 +1,8 @@
+from abc import ABC
+
+
+class AbstractOsNotification(ABC):
+    def send_notification(self, title: str, message: str):
+        """
+        Shows an OS-native notification to the user
+        """
diff --git a/focus_time_app/utils/os_notification/macos_os_notification.py b/focus_time_app/utils/os_notification/macos_os_notification.py
new file mode 100644
index 0000000..d9ecca6
--- /dev/null
+++ b/focus_time_app/utils/os_notification/macos_os_notification.py
@@ -0,0 +1,13 @@
+# from mac_notifications import client
+import os
+
+from focus_time_app.utils.os_notification import AbstractOsNotification
+
+
+class MacosOsNotification(AbstractOsNotification):
+    def send_notification(self, title: str, message: str):
+        # client.create_notification(title=title, text=message)  # Note: we could also set an icon, if we wanted to
+        # TODO: replace this approach with https://pypi.org/project/macos-notifications
+        #  once https://github.com/Jorricks/macos-notifications/issues/12 is resolved
+        appleScriptNotification = f'display notification "{message}" with title "{title}"'
+        os.system(f"osascript -e '{appleScriptNotification}'")
diff --git a/focus_time_app/utils/os_notification/win_os_notification.py b/focus_time_app/utils/os_notification/win_os_notification.py
new file mode 100644
index 0000000..a976a88
--- /dev/null
+++ b/focus_time_app/utils/os_notification/win_os_notification.py
@@ -0,0 +1,11 @@
+from windows_toasts import WindowsToaster, Toast
+
+from focus_time_app.utils.os_notification import AbstractOsNotification
+
+
+class WinOsNotification(AbstractOsNotification):
+    def send_notification(self, title: str, message: str):
+        toaster = WindowsToaster('Focus Time App')
+        t = Toast()
+        t.text_fields = [title, message]
+        toaster.show_toast(t)
diff --git a/requirements.txt b/requirements.txt
index 8f9ef96..96a2907 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,3 +10,5 @@ pytest==7.4.1
 selenium==4.12.0
 caldav==1.3.6
 pwinput==1.0.3
+windows-toasts==1.0.0; platform_system == "Windows"
+macos-notifications==0.1.6; platform_system == "Darwin"
diff --git a/tests/conftest.py b/tests/conftest.py
index c10e67e..32c988a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -46,8 +46,11 @@ def start_commands(tmp_path: Path) -> ConfiguredCommands:
         return ConfiguredCommands(commands=["dnd-start", f"echo start>> {verification_file_path}"],
                                   verification_file_path=verification_file_path)
     if sys.platform == "darwin":
-        return ConfiguredCommands(commands=[f"echo start >> {verification_file_path}"],
-                                  verification_file_path=verification_file_path)
+        commands = [f"echo start >> {verification_file_path}"]
+        if CommandExecutorImpl.is_dnd_helper_installed():
+            commands.insert(0, "dnd-start")
+
+        return ConfiguredCommands(commands=commands, verification_file_path=verification_file_path)
     raise NotImplementedError
 
 
@@ -63,8 +66,11 @@ def stop_commands(tmp_path: Path) -> ConfiguredCommands:
         return ConfiguredCommands(commands=["dnd-stop", f"echo stop>> {verification_file_path}"],
                                   verification_file_path=verification_file_path)
     elif sys.platform == "darwin":
-        return ConfiguredCommands(commands=[f"echo stop >> {verification_file_path}"],
-                                  verification_file_path=verification_file_path)
+        commands = [f"echo stop >> {verification_file_path}"]
+        if CommandExecutorImpl.is_dnd_helper_installed():
+            commands.insert(0, "dnd-stop")
+
+        return ConfiguredCommands(commands=commands, verification_file_path=verification_file_path)
     raise NotImplementedError
 
 
@@ -101,7 +107,7 @@ def configured_calendar_adapter(request, start_commands, stop_commands) -> Abstr
                              focustime_event_name=focustime_event_name,
                              start_commands=start_commands.commands, stop_commands=stop_commands.commands,
                              dnd_profile_name=dnd_profile_name, set_event_reminder=True,
-                             event_reminder_time_minutes=15)
+                             event_reminder_time_minutes=15, show_notification=False)
 
     return get_configured_calendar_adapter_for_testing(config)
 
@@ -121,7 +127,7 @@ def configured_cli(calendar_type: CalendarType, skip_background_scheduler_setup:
                              focustime_event_name=focustime_event_name,
                              start_commands=start_commands.commands, stop_commands=stop_commands.commands,
                              dnd_profile_name=dnd_profile_name, set_event_reminder=True,
-                             event_reminder_time_minutes=15)
+                             event_reminder_time_minutes=15, show_notification=True)
 
     Persistence.get_config_file_path().unlink(missing_ok=True)
 
@@ -167,6 +173,9 @@ def configured_cli(calendar_type: CalendarType, skip_background_scheduler_setup:
         out = config_process.stdout.readline()  # asks for reminder minutes
         write_line_to_stream(config_process.stdin, config.event_reminder_time_minutes)
 
+    out = config_process.stdout.readline()  # asks whether to show a notification
+    write_line_to_stream(config_process.stdin, "y" if config.show_notification else "n")
+
     if sys.platform == "win32":
         out = config_process.stdout.readline()  # asks for name of Windows Focus Assist profile
         write_line_to_stream(config_process.stdin, config.dnd_profile_name)
diff --git a/tests/end2end/test_start_stop.py b/tests/end2end/test_start_stop.py
index 880c9a0..5f7e7e5 100644
--- a/tests/end2end/test_start_stop.py
+++ b/tests/end2end/test_start_stop.py
@@ -30,7 +30,7 @@ def test_start_stop_simple(self, configured_cli_no_bg_jobs: ConfiguredCLI):
 
         focus_time_duration_minutes = 2
         output = run_cli_command_handle_output_error("start", additional_args=[str(focus_time_duration_minutes)])
-        assert output.startswith("Found a new focus time, calling start command(s) ...")
+        assert "calling start command(s) ..." in output
 
         if CommandExecutorImpl.is_dnd_helper_installed():
             assert CommandExecutorImpl.is_dnd_active()
@@ -56,7 +56,7 @@ def test_start_stop_simple(self, configured_cli_no_bg_jobs: ConfiguredCLI):
 
         # Run the "stop" command, verify that DND is then disabled
         output = run_cli_command_handle_output_error("stop")
-        assert output.startswith("No focus time is active, calling stop command(s) ...")
+        assert output.startswith("No focus time is active anymore, calling stop command(s) ...")
 
         if CommandExecutorImpl.is_dnd_helper_installed():
             assert not CommandExecutorImpl.is_dnd_active()
diff --git a/tests/end2end/test_sync.py b/tests/end2end/test_sync.py
index 4f3baaa..b0164a7 100644
--- a/tests/end2end/test_sync.py
+++ b/tests/end2end/test_sync.py
@@ -49,8 +49,7 @@ def test_manual_on_off_sync(self, configured_cli_no_bg_jobs: ConfiguredCLI):
         time.sleep(60)
 
         # run sync, should enable DND
-        assert run_cli_command_handle_output_error("sync").startswith(
-            "Found a new focus time, calling start command(s) ...")
+        assert "calling start command(s) ..." in run_cli_command_handle_output_error("sync")
         if CommandExecutorImpl.is_dnd_helper_installed():
             assert CommandExecutorImpl.is_dnd_active()
         assert configured_cli_no_bg_jobs.verification_file_path.read_text() == "start\n"
@@ -67,7 +66,7 @@ def test_manual_on_off_sync(self, configured_cli_no_bg_jobs: ConfiguredCLI):
 
         # run sync again, DND should be turned off
         assert run_cli_command_handle_output_error("sync").startswith(
-            "No focus time is active, calling stop command(s) ...")
+            "No focus time is active anymore, calling stop command(s) ...")
         if CommandExecutorImpl.is_dnd_helper_installed():
             assert not CommandExecutorImpl.is_dnd_active()
         assert configured_cli_no_bg_jobs.verification_file_path.read_text() == "start\nstop\n"
@@ -143,8 +142,7 @@ def test_reminder(self, configured_cli_no_bg_jobs: ConfiguredCLI):
         assert events[0].reminder_in_minutes == new_event_reminder_time_minutes
 
         # The sync call should set the event reminder time
-        assert run_cli_command_handle_output_error("sync").startswith(
-            "Found a new focus time, calling start command(s) ...")
+        assert "calling start command(s) ..." in run_cli_command_handle_output_error("sync")
 
         events = configured_cli_no_bg_jobs.calendar_adapter.get_events((now - timedelta(minutes=1),
                                                                         now + timedelta(minutes=2)))
diff --git a/tests/test_persistence.py b/tests/test_persistence.py
index 3f9451b..5ff0f62 100644
--- a/tests/test_persistence.py
+++ b/tests/test_persistence.py
@@ -18,7 +18,7 @@ def test_store_load_configuration(self):
         config = ConfigurationV1(calendar_type=CalendarType.Outlook365, calendar_look_ahead_hours=3,
                                  calendar_look_back_hours=5, focustime_event_name="ft", start_commands=["start"],
                                  stop_commands=["stop"], dnd_profile_name="dnd", set_event_reminder=True,
-                                 event_reminder_time_minutes=15)
+                                 event_reminder_time_minutes=15, show_notification=False)
         Persistence.store_configuration(config)
 
         config_loaded = Persistence.load_configuration()