diff --git a/src/python/matrix_client.py b/src/python/matrix_client.py
index 704f8f55..dd84acd0 100644
--- a/src/python/matrix_client.py
+++ b/src/python/matrix_client.py
@@ -19,6 +19,7 @@ from . import __about__, utils
 from .html_filter import HTML_FILTER
 from .models.items import Account, Event, Member, Room, TypeSpecifier
 from .models.model_store import ModelStore
+from .pyotherside_events import AlertRequested
 
 
 class UploadError(Enum):
@@ -52,6 +53,7 @@ class MatrixClient(nio.AsyncClient):
 
         self.sync_task:           Optional[asyncio.Future] = None
         self.first_sync_happened: asyncio.Event            = asyncio.Event()
+        self.first_sync_date:     Optional[datetime]       = None
 
         self.send_locks: DefaultDict[str, asyncio.Lock] = \
                 DefaultDict(asyncio.Lock)  # {room_id: lock}
@@ -299,6 +301,17 @@ class MatrixClient(nio.AsyncClient):
 
     # Functions to register data into models
 
+    async def event_is_past(self, ev: Union[nio.Event, Event]) -> bool:
+        if not self.first_sync_date:
+            return True
+
+        if isinstance(ev, Event):
+            return ev.date < self.first_sync_date
+
+        date = datetime.fromtimestamp(ev.server_timestamp / 1000)
+        return date < self.first_sync_date
+
+
     async def set_room_last_event(self, room_id: str, item: Event) -> None:
         room = self.models[Room, self.user_id][room_id]
 
@@ -446,6 +459,9 @@ class MatrixClient(nio.AsyncClient):
             with suppress(KeyError):
                 item.client_id = f"echo-{client.resolved_echoes[ev.event_id]}"
 
+        elif not await self.event_is_past(ev):
+            AlertRequested()
+
         self.models[Event, self.user_id, room.room_id][item.client_id] = item
 
         await self.set_room_last_event(room.room_id, item)
@@ -476,7 +492,8 @@ class MatrixClient(nio.AsyncClient):
         if not self.first_sync_happened.is_set():
             asyncio.ensure_future(self.load_rooms_without_visible_events())
 
-        self.first_sync_happened.set()
+            self.first_sync_happened.set()
+            self.first_sync_date = datetime.now()
 
 
     async def onErrorResponse(self, resp: nio.ErrorResponse) -> None:
diff --git a/src/python/pyotherside_events.py b/src/python/pyotherside_events.py
index 4c685900..0c5f8574 100644
--- a/src/python/pyotherside_events.py
+++ b/src/python/pyotherside_events.py
@@ -8,6 +8,8 @@ from .models import SyncId
 
 @dataclass
 class PyOtherSideEvent:
+    """Event that will be sent to QML by PyOtherSide."""
+
     def __post_init__(self) -> None:
         # CPython >= 3.6 or any Python >= 3.7 needed for correct dict order
         args = [
@@ -27,17 +29,36 @@ class PyOtherSideEvent:
 
 @dataclass
 class ExitRequested(PyOtherSideEvent):
+    """Request for the application to exit."""
+
     exit_code: int = 0
 
 
+@dataclass
+class AlertRequested(PyOtherSideEvent):
+    """Request an alert to be shown for msec milliseconds.
+    If msec is 0 (default), the alert should be shown indefinitely until
+    the window is focused.
+
+    The Alert state for example sets the urgency hint on X11/Wayland,
+    or flashes the taskbar icon on Windows.
+    """
+
+    msec: int = 0
+
+
 @dataclass
 class CoroutineDone(PyOtherSideEvent):
+    """Indicate that an asyncio coroutine finished."""
+
     uuid:   str = field()
     result: Any = None
 
 
 @dataclass
 class ModelUpdated(PyOtherSideEvent):
+    """Indicate that a backend model's data changed."""
+
     sync_id: SyncId               = field()
     data:    List[Dict[str, Any]] = field()
 
diff --git a/src/qml/event_handlers.js b/src/qml/event_handlers.js
index 0f9f95e6..78c1b120 100644
--- a/src/qml/event_handlers.js
+++ b/src/qml/event_handlers.js
@@ -6,6 +6,11 @@ function onExitRequested(exitCode) {
 }
 
 
+function onAlertRequested(msec) {
+    window.alert(msec)
+}
+
+
 function onCoroutineDone(uuid, result) {
     py.pendingCoroutines[uuid](result)
     delete pendingCoroutines[uuid]