diff --git a/PortMaster/pylibs/pugscene.py b/PortMaster/pylibs/pugscene.py
index 6855f08..58fe6f0 100644
--- a/PortMaster/pylibs/pugscene.py
+++ b/PortMaster/pylibs/pugscene.py
@@ -22,6 +22,50 @@
 _ = gettext.gettext
 
 
+def get_startup_warnings(device_info):
+    """
+    Check for unsupported configurations that should warn the user.
+
+    Returns a list of (keyword, reason, suggestion) tuples describing each problem.
+    """
+    warnings = []
+
+    firmware_suggestion = _('For the best experience, switch to a supported firmware such as muOS or KNULLI.')
+
+    # Unsupported firmware checks, most-specific first
+    if Path('/mnt/SDCARD/spruce/').exists():
+        warnings.append(('spruce', _('SpruceOS is not supported by PortMaster.'), firmware_suggestion))
+
+    try:
+        if 'CrossMix-OS' in Path('/mnt/SDCARD/autorun.inf').read_text():
+            warnings.append(('crossmix', _('CrossMix-OS is not supported by PortMaster.'), firmware_suggestion))
+    except (OSError, UnicodeDecodeError):
+        pass
+
+    # TODO: add checks for NextUI, PakUI when we have unique markers
+
+    # Generic catch-all for TrimUI-based OSes we can't identify specifically
+    if not warnings and Path('/etc/trimui_device.txt').exists():
+        warnings.append(('trimui', _('Your OS is not supported by PortMaster.'), firmware_suggestion))
+
+    # Low RAM check
+    if device_info.get('ram', 1024) < 1024:
+        warnings.append(('lowram', _('Your device has less than 1GB of RAM.'), None))
+
+    return warnings
+
+
+def get_next_warning_time():
+    """
+    Returns an ISO date string for when to show the warning again.
+    """
+    import random
+    import datetime
+
+    next_warning = datetime.datetime.now() + datetime.timedelta(days=random.choice([5, 7, 11, 13]))
+    return next_warning.date().isoformat()
+
+
 class StringFormatter:
     def __init__(self, data_dict):
         self.data_dict = data_dict
@@ -384,6 +428,8 @@ def __init__(self, gui):
         self.set_buttons({})
 
     def do_update(self, events):
+        import datetime
+
         self.scene_deactivate()
         self.gui.updated = True
 
@@ -395,9 +441,17 @@ def do_update(self, events):
                 ]
 
         else:
-            self.gui.scenes = [
-                ('root', [MainMenuScene(self.gui)]),
-                ]
+            warnings = get_startup_warnings(harbourmaster.device_info())
+            warning_time = cfg_data.get('warning_time', '')
+
+            if warnings and warning_time < datetime.datetime.now().date().isoformat():
+                self.gui.scenes = [
+                    ('root', [StartupWarningScene(self.gui, warnings)]),
+                    ]
+            else:
+                self.gui.scenes = [
+                    ('root', [MainMenuScene(self.gui)]),
+                    ]
 
         return True
 
@@ -451,6 +505,89 @@ def do_update(self, events):
                 cfg_data['disclaimer'] = True
                 self.gui.save_config(cfg_data)
 
+                self.scene_deactivate()
+                self.gui.updated = True
+
+                warnings = get_startup_warnings(harbourmaster.device_info())
+                if warnings:
+                    self.gui.scenes = [
+                        ('root', [StartupWarningScene(self.gui, warnings)]),
+                        ]
+                else:
+                    self.gui.scenes = [
+                        ('root', [MainMenuScene(self.gui)]),
+                        ]
+
+                return True
+
+            if events.was_pressed('B'):
+                self.button_back()
+                if self.gui.message_box(
+                        _("Are you sure you want to exit PortMaster?"),
+                        want_cancel=True):
+
+                    self.gui.do_cancel()
+                    return True
+
+
+class StartupWarningScene(BaseScene):
+
+    def __init__(self, gui, warnings):
+        super().__init__(gui)
+        self.scene_title = _("Warning")
+
+        ## Wait x seconds.
+        self.warning_wait = 10
+
+        self.load_regions("disclaimer", ['disclaimer_text'])
+
+        # Build message from warnings: each reason, then suggestions, then common footer
+        parts = []
+        suggestions = []
+        for keyword, reason, suggestion in warnings:
+            parts.append(reason)
+            if suggestion is not None and suggestion not in suggestions:
+                suggestions.append(suggestion)
+
+        parts.append(_('Many ports will not work.'))
+
+        if suggestions:
+            parts.append('')
+            parts.extend(suggestions)
+
+        self.tags['disclaimer_text'].text = '\n'.join(parts)
+        self.tags['disclaimer_text'].fontsize = int(self.tags['disclaimer_text'].fontsize * 1.5)
+
+        self.last_elapsed = None
+
+    def do_draw(self):
+        elapsed = self.gui.timers.since('warning_wait') // 1000
+
+        elapsed = min(elapsed, self.warning_wait)
+
+        if elapsed != self.last_elapsed:
+            if elapsed < self.warning_wait:
+                self.tags['button_bar'].bar = [f'Wait {self.warning_wait - elapsed} seconds']
+            else:
+                self.set_buttons({'A': _('I Understand'), 'B': _('Quit')})
+
+            self.last_elapsed = elapsed
+
+        super().do_draw()
+
+    def do_update(self, events):
+        super().do_update(events)
+
+        elapsed = self.gui.timers.since('warning_wait') // 1000
+
+        elapsed = min(elapsed, self.warning_wait)
+
+        if elapsed == self.warning_wait:
+            if events.was_pressed('A'):
+                cfg_data = self.gui.get_config()
+                cfg_data['warning_time'] = get_next_warning_time()
+                self.gui.save_config(cfg_data)
+
                 self.scene_deactivate()
                 self.gui.updated = True
                 self.gui.scenes = [