diff --git a/KVMConsoleiPad/Input/PhysicalKeyboardObserver.swift b/KVMConsoleiPad/Input/PhysicalKeyboardObserver.swift
new file mode 100644
index 0000000..37bf9af
--- /dev/null
+++ b/KVMConsoleiPad/Input/PhysicalKeyboardObserver.swift
@@ -0,0 +1,51 @@
+import Combine
+import GameController
+
+/// Tracks whether a hardware keyboard is currently attached to the device.
+///
+/// The on-screen modifier-key bar exists so that touch/on-screen-keyboard users
+/// can send Ctrl/Alt/Cmd/etc. When a physical keyboard is connected those keys
+/// are already available, so the bar is redundant and the viewer hides it.
+@MainActor
+final class PhysicalKeyboardObserver: ObservableObject {
+    @Published private(set) var isConnected: Bool
+
+    private var observers: [NSObjectProtocol] = []
+
+    init() {
+        isConnected = GCKeyboard.coalesced != nil
+
+        let center = NotificationCenter.default
+        observers.append(center.addObserver(
+            forName: .GCKeyboardDidConnect,
+            object: nil,
+            queue: .main
+        ) { [weak self] _ in
+            MainActor.assumeIsolated { self?.isConnected = true }
+        })
+        observers.append(center.addObserver(
+            forName: .GCKeyboardDidDisconnect,
+            object: nil,
+            queue: .main
+        ) { [weak self] _ in
+            // A disconnect notification can fire while another keyboard is still
+            // attached, so re-read the coalesced keyboard rather than assuming none.
+            MainActor.assumeIsolated { self?.isConnected = GCKeyboard.coalesced != nil }
+        })
+    }
+
+    deinit {
+        for observer in observers {
+            NotificationCenter.default.removeObserver(observer)
+        }
+    }
+}
+
+/// Resolves whether the modifier-key bar should be visible. Kept as a pure
+/// function so the precedence rule (hardware keyboard wins over the user toggle)
+/// is unit-testable without a live `GCKeyboard`.
+enum ModifierBarVisibility {
+    static func shouldShow(userEnabled: Bool, physicalKeyboardConnected: Bool) -> Bool {
+        userEnabled && !physicalKeyboardConnected
+    }
+}
diff --git a/KVMConsoleiPad/UI/ViewerView.swift b/KVMConsoleiPad/UI/ViewerView.swift
index 62486e6..dc8420d 100644
--- a/KVMConsoleiPad/UI/ViewerView.swift
+++ b/KVMConsoleiPad/UI/ViewerView.swift
@@ -33,6 +33,7 @@ struct ViewerHostView: View {
 
 struct ViewerView: View {
     @StateObject private var model: ViewerViewModel
+    @StateObject private var keyboardObserver = PhysicalKeyboardObserver()
     @State private var modifierState = ModifierKeyState()
     @State private var showModifierBar = true
     @State private var keyboardFocusToken = 0
@@ -54,7 +55,7 @@ struct ViewerView: View {
                 errorOverlay
             }
 
-            if showModifierBar, model.passwordPrompt == nil, !showsErrorOverlay {
+            if modifierBarVisible, model.passwordPrompt == nil, !showsErrorOverlay {
                 ModifierKeyBar(state: $modifierState) { usage, modifier in
                     sendVirtualKey(usage: usage, modifier: modifier)
                 }
@@ -120,6 +121,13 @@ struct ViewerView: View {
         }
     }
 
+    private var modifierBarVisible: Bool {
+        ModifierBarVisibility.shouldShow(
+            userEnabled: showModifierBar,
+            physicalKeyboardConnected: keyboardObserver.isConnected
+        )
+    }
+
     private var showsLocalCursor: Bool {
         model.isStreaming
             && model.isMouseCaptureEnabled
@@ -171,7 +179,10 @@ struct ViewerView: View {
             }
             .toggleStyle(.button)
             .labelStyle(.iconOnly)
-            .help(showModifierBar ? "Hide modifier-key bar" : "Show modifier-key bar")
+            .disabled(keyboardObserver.isConnected)
+            .help(keyboardObserver.isConnected
+                  ? "Hardware keyboard connected — modifier-key bar hidden"
+                  : (showModifierBar ? "Hide modifier-key bar" : "Show modifier-key bar"))
 
             Button {
                 keyboardFocusToken += 1
diff --git a/KVMConsoleiPadTests/NanoKVMiPadTests.swift b/KVMConsoleiPadTests/NanoKVMiPadTests.swift
index 5dbc546..2baf3ba 100644
--- a/KVMConsoleiPadTests/NanoKVMiPadTests.swift
+++ b/KVMConsoleiPadTests/NanoKVMiPadTests.swift
@@ -58,4 +58,22 @@ final class KVMConsoleiPadTests: XCTestCase {
         XCTAssertFalse(PointerScrollResolver.shouldEmitWheel(touchCount: 1))
         XCTAssertTrue(PointerScrollResolver.shouldEmitWheel(touchCount: 2))
     }
+
+    func test_modifierBarHiddenWhenPhysicalKeyboardConnected() {
+        XCTAssertFalse(
+            ModifierBarVisibility.shouldShow(userEnabled: true, physicalKeyboardConnected: true)
+        )
+    }
+
+    func test_modifierBarVisibleWhenEnabledAndNoPhysicalKeyboard() {
+        XCTAssertTrue(
+            ModifierBarVisibility.shouldShow(userEnabled: true, physicalKeyboardConnected: false)
+        )
+    }
+
+    func test_modifierBarHiddenWhenUserDisablesIt() {
+        XCTAssertFalse(
+            ModifierBarVisibility.shouldShow(userEnabled: false, physicalKeyboardConnected: false)
+        )
+    }
 }