diff --git a/zx/_device.py b/zx/_device.py
index 281a1e3..40defff 100644
--- a/zx/_device.py
+++ b/zx/_device.py
@@ -11,11 +11,25 @@
 import enum
 
 
-class DeviceEvent(enum.Enum):
-    PAUSE_STATE_UPDATED = enum.auto()
-    QUANTUM_RUN = enum.auto()
-    SCREEN_UPDATED = enum.auto()
-    TAPE_STATE_UPDATED = enum.auto()
+class DeviceEvent(object):
+    pass
+
+
+class PauseStateUpdated(DeviceEvent):
+    pass
+
+
+class QuantumRun(DeviceEvent):
+    pass
+
+
+class ScreenUpdated(DeviceEvent):
+    def __init__(self, pixels):
+        self.pixels = pixels
+
+
+class TapeStateUpdated(DeviceEvent):
+    pass
 
 
 class Device(object):
diff --git a/zx/_emulator.py b/zx/_emulator.py
index 3ff7dfb..29b0c19 100644
--- a/zx/_emulator.py
+++ b/zx/_emulator.py
@@ -12,7 +12,10 @@
 import time
 from ._data import MachineSnapshot
 from ._data import SoundFile
-from ._device import DeviceEvent
+from ._device import PauseStateUpdated
+from ._device import QuantumRun
+from ._device import ScreenUpdated
+from ._device import TapeStateUpdated
 from ._error import Error
 from ._except import EmulatorException
 from ._file import parse_file
@@ -85,14 +88,10 @@ def __init__(self, speed_factor=1.0, profile=None, devices=None):
     def _is_paused(self):
         return self.__is_paused_flag
 
-    def __notify(self, id, *args):
-        for device in self.__devices:
-            device._on_emulator_event(id, *args)
-
     # TODO: Double-underscore or make public.
     def _pause(self, is_paused=True):
         self.__is_paused_flag = is_paused
-        self.__notify(DeviceEvent.PAUSE_STATE_UPDATED)
+        self.notify_devices(PauseStateUpdated())
 
     # TODO: Double-underscore or make public.
     def _toggle_pause(self):
@@ -115,7 +114,7 @@ def _is_tape_paused(self):
 
     def __pause_tape(self, is_paused=True):
         self._tape_player.pause(is_paused)
-        self.__notify(DeviceEvent.TAPE_STATE_UPDATED)
+        self.notify_devices(TapeStateUpdated())
 
     def __unpause_tape(self):
         self.__pause_tape(is_paused=False)
@@ -293,7 +292,7 @@ def __run_quantum(self, speed_factor=None):
             creator_info = self.__playback_player.find_recording_info_chunk()
 
         if True:  # TODO
-            self.__notify(DeviceEvent.QUANTUM_RUN)
+            self.notify_devices(QuantumRun())
 
             # TODO: For debug purposes.
             '''
@@ -338,7 +337,7 @@ def __run_quantum(self, speed_factor=None):
                 self.render_screen()
 
                 pixels = self.get_frame_pixels()
-                self.__notify(DeviceEvent.SCREEN_UPDATED, pixels)
+                self.notify_devices(ScreenUpdated(pixels))
 
                 self._tape_player.skip_rest_of_frame()
                 self._emulation_time.advance(1 / 50)
diff --git a/zx/_gui.py b/zx/_gui.py
index a8099ca..11d27af 100644
--- a/zx/_gui.py
+++ b/zx/_gui.py
@@ -11,7 +11,10 @@
 import cairo
 import gi
 from ._device import Device
-from ._device import DeviceEvent
+from ._device import PauseStateUpdated
+from ._device import QuantumRun
+from ._device import ScreenUpdated
+from ._device import TapeStateUpdated
 from ._error import USER_ERRORS
 from ._error import verbalize_error
 from ._except import EmulationExit
@@ -181,11 +184,11 @@ def __init__(self, emulator):
             'PAUSE': self.emulator._toggle_pause,
         }
 
-        self._EMULATOR_EVENT_HANDLERS = {
-            DeviceEvent.PAUSE_STATE_UPDATED: self._on_updated_pause_state,
-            DeviceEvent.QUANTUM_RUN: self._on_quantum_run,
-            DeviceEvent.SCREEN_UPDATED: self._on_updated_screen,
-            DeviceEvent.TAPE_STATE_UPDATED: self._on_updated_tape_state,
+        self._EVENT_HANDLERS = {
+            PauseStateUpdated: self._on_updated_pause_state,
+            QuantumRun: self._on_quantum_run,
+            ScreenUpdated: self._on_updated_screen,
+            TapeStateUpdated: self._on_updated_tape_state,
         }
 
         self._notification = Notification()
@@ -259,8 +262,8 @@ def _on_draw_area(self, widget, context):
 
         self._screencast.on_draw(context.get_group_target())
 
-    def _on_updated_screen(self, pixels):
-        self.frame_data[:] = pixels
+    def _on_updated_screen(self, event):
+        self.frame_data[:] = event.pixels
         self.area.queue_draw()
 
     def _show_help(self):
@@ -368,24 +371,24 @@ def _on_window_state_event(self, widget, event):
         state = event.new_window_state
         self._is_fullscreen = bool(state & Gdk.WindowState.FULLSCREEN)
 
-    def _on_emulator_event(self, id, *args):
-        self._EMULATOR_EVENT_HANDLERS[id](*args)
+    def on_event(self, event):
+        self._EVENT_HANDLERS[type(event)](event)
 
-    def _on_updated_pause_state(self):
+    def _on_updated_pause_state(self, event):
         if self.emulator._is_paused():
             self._notification.set(draw_pause_notification,
                                    self.emulator._emulation_time)
         else:
             self._notification.clear()
 
-    def _on_updated_tape_state(self):
+    def _on_updated_tape_state(self, event):
         tape_paused = self.emulator._is_tape_paused()
         draw = (draw_tape_pause_notification if tape_paused
                 else draw_tape_resume_notification)
         tape_time = self.emulator._tape_player.get_time()
         self._notification.set(draw, tape_time)
 
-    def _on_quantum_run(self):
+    def _on_quantum_run(self, event):
         if self._queued_exception is not None:
             e = self._queued_exception
             self._queued_exception = None
diff --git a/zx/_machine.py b/zx/_machine.py
index fa7c7d4..80cc412 100644
--- a/zx/_machine.py
+++ b/zx/_machine.py
@@ -366,6 +366,10 @@ def __exit__(self, type, value, tb):
     def stop(self):
         raise EmulationExit()
 
+    def notify_devices(self, event):
+        for device in self.devices:
+            device.on_event(event)
+
     def set_breakpoints(self, addr, size):
         self.mark_addrs(addr, size, self._BREAKPOINT_MARK)