diff --git a/packages/debugger-shell/src/node/index.flow.js b/packages/debugger-shell/src/node/index.flow.js
index 7c4e06831c5036..476cf33656bc15 100644
--- a/packages/debugger-shell/src/node/index.flow.js
+++ b/packages/debugger-shell/src/node/index.flow.js
@@ -29,7 +29,7 @@ async function unstable_spawnDebuggerShellWithArgs(
   args: string[],
   {
     mode = 'detached',
-    flavor = 'prebuilt',
+    flavor = process.env.RNDT_DEV === '1' ? 'dev' : 'prebuilt',
     prebuiltBinaryPath,
   }: $ReadOnly<{
     // In 'syncAndExit' mode, the current process will block until the spawned process exits, and then it will exit
@@ -38,7 +38,7 @@ async function unstable_spawnDebuggerShellWithArgs(
     // continue to run normally.
     mode?: 'syncThenExit' | 'detached',
     flavor?: DebuggerShellFlavor,
-    prebuiltBinaryPath?: string,
+    prebuiltBinaryPath?: ?string,
   }> = {},
 ): Promise<void> {
   const [binaryPath, baseArgs] = getShellBinaryAndArgs(
@@ -51,6 +51,13 @@ async function unstable_spawnDebuggerShellWithArgs(
       stdio: 'inherit',
       windowsHide: true,
       detached: mode === 'detached',
+      env: {
+        ...process.env,
+        // If this package is used in an Electron app (e.g. inside a VS Code extension),
+        // ELECTRON_RUN_AS_NODE=1 can leak from the parent process.
+        // Since this is never the right way to launch the Fusebox shell, we guard against it here.
+        ELECTRON_RUN_AS_NODE: '',
+      },
     });
     if (mode === 'detached') {
       child.on('spawn', () => {
@@ -112,10 +119,13 @@ export type DebuggerShellPreparationResult = $ReadOnly<{
  * instantly when the user tries to open it (and conversely, the user is
  * informed ASAP if it is not ready to use).
  */
-async function unstable_prepareDebuggerShell(
-  flavor: DebuggerShellFlavor,
-  {prebuiltBinaryPath}: {prebuiltBinaryPath?: string} = {},
-): Promise<DebuggerShellPreparationResult> {
+async function unstable_prepareDebuggerShell({
+  prebuiltBinaryPath,
+  flavor = process.env.RNDT_DEV === '1' ? 'dev' : 'prebuilt',
+}: {
+  prebuiltBinaryPath?: ?string,
+  flavor?: DebuggerShellFlavor,
+} = {}): Promise<DebuggerShellPreparationResult> {
   try {
     switch (flavor) {
       case 'prebuilt':
diff --git a/packages/dev-middleware/src/createDevMiddleware.js b/packages/dev-middleware/src/createDevMiddleware.js
index 72d1bdd52de000..9afc7c1aa12690 100644
--- a/packages/dev-middleware/src/createDevMiddleware.js
+++ b/packages/dev-middleware/src/createDevMiddleware.js
@@ -9,6 +9,7 @@
  */
 
 import type {CreateCustomMessageHandlerFn} from './inspector-proxy/CustomMessageHandler';
+import type {HasConnectedDevicesListener} from './inspector-proxy/InspectorProxy';
 import type {BrowserLauncher} from './types/BrowserLauncher';
 import type {EventReporter, ReportableEvent} from './types/EventReporter';
 import type {Experiments, ExperimentsConfig} from './types/Experiments';
@@ -73,6 +74,8 @@ type Options = $ReadOnly<{
 type DevMiddlewareAPI = $ReadOnly<{
   middleware: NextHandleFunction,
   websocketEndpoints: {[path: string]: ws$WebSocketServer},
+  unstable_hasConnectedDevices(): boolean,
+  unstable_addHasConnectedDevicesListener: HasConnectedDevicesListener,
 }>;
 
 export default function createDevMiddleware({
@@ -131,6 +134,10 @@ export default function createDevMiddleware({
   return {
     middleware,
     websocketEndpoints: inspectorProxy.createWebSocketListeners(),
+    unstable_hasConnectedDevices: () =>
+      inspectorProxy.unstable_hasConnectedDevices(),
+    unstable_addHasConnectedDevicesListener: cb =>
+      inspectorProxy.unstable_addHasConnectedDevicesListener(cb),
   };
 }
 
diff --git a/packages/dev-middleware/src/inspector-proxy/InspectorProxy.js b/packages/dev-middleware/src/inspector-proxy/InspectorProxy.js
index f9f419b1124d75..77343a19b458d9 100644
--- a/packages/dev-middleware/src/inspector-proxy/InspectorProxy.js
+++ b/packages/dev-middleware/src/inspector-proxy/InspectorProxy.js
@@ -71,6 +71,12 @@ export interface InspectorProxyQueries {
   ): Array<PageDescription>;
 }
 
+export type RemoveHasConnectedDevicesListener = () => void;
+
+export type HasConnectedDevicesListener = (
+  callback: (hasConnectedDevices: boolean) => void,
+) => RemoveHasConnectedDevicesListener;
+
 /**
  * Main Inspector Proxy class that connects JavaScript VM inside Android/iOS apps and JS debugger.
  */
@@ -97,6 +103,8 @@ export default class InspectorProxy implements InspectorProxyQueries {
 
   #eventLoopPerfTracker: EventLoopPerfTracker;
 
+  #onHasConnectedDevicesChangedFns: Set<(boolean) => void>;
+
   constructor(
     serverBaseUrl: string,
     eventReporter: ?EventReporter,
@@ -111,6 +119,7 @@ export default class InspectorProxy implements InspectorProxyQueries {
     this.#experiments = experiments;
     this.#logger = logger;
     this.#customMessageHandler = customMessageHandler;
+    this.#onHasConnectedDevicesChangedFns = new Set();
     if (trackEventLoopPerf) {
       this.#eventLoopPerfTracker = new EventLoopPerfTracker({
         perfMeasurementDuration: EVENT_LOOP_PERF_MEASUREMENT_MS,
@@ -142,6 +151,18 @@ export default class InspectorProxy implements InspectorProxyQueries {
     }
   }
 
+  unstable_hasConnectedDevices(): boolean {
+    return this.#devices.size > 0;
+  }
+
+  unstable_addHasConnectedDevicesListener: HasConnectedDevicesListener =
+    onDevicesChanged => {
+      this.#onHasConnectedDevicesChangedFns.add(onDevicesChanged);
+      return () => {
+        this.#onHasConnectedDevicesChangedFns.delete(onDevicesChanged);
+      };
+    };
+
   getPageDescriptions({
     requestorRelativeBaseUrl,
     logNoPagesForConnectedDevice = false,
@@ -365,6 +386,9 @@ export default class InspectorProxy implements InspectorProxyQueries {
         }
 
         this.#devices.set(deviceId, newDevice);
+        if (this.#devices.size === 1) {
+          this.#onHasConnectedDevicesChangedFns.forEach(cb => cb(true));
+        }
 
         debug(
           "Got new device connection: name='%s', app=%s, device=%s, via=%s",
@@ -457,6 +481,9 @@ export default class InspectorProxy implements InspectorProxyQueries {
 
           if (this.#devices.get(deviceId)?.dangerouslyGetSocket() === socket) {
             this.#devices.delete(deviceId);
+            if (this.#devices.size === 0) {
+              this.#onHasConnectedDevicesChangedFns.forEach(cb => cb(false));
+            }
           }
         });
       } catch (error) {
diff --git a/packages/dev-middleware/src/utils/DefaultBrowserLauncher.js b/packages/dev-middleware/src/utils/DefaultBrowserLauncher.js
index dfe393c409f1b9..ee43ddb48d7e11 100644
--- a/packages/dev-middleware/src/utils/DefaultBrowserLauncher.js
+++ b/packages/dev-middleware/src/utils/DefaultBrowserLauncher.js
@@ -73,19 +73,16 @@ const DefaultBrowserLauncher = {
     url: string,
     windowKey: string,
   ): Promise<void> {
-    return await unstable_spawnDebuggerShellWithArgs(
-      ['--frontendUrl=' + url, '--windowKey=' + windowKey],
-      {
-        mode: 'detached',
-        flavor: process.env.RNDT_DEV === '1' ? 'dev' : 'prebuilt',
-      },
-    );
+    return await unstable_spawnDebuggerShellWithArgs([
+      '--frontendUrl=' + url,
+      '--windowKey=' + windowKey,
+    ]);
   },
 
-  async unstable_prepareFuseboxShell(): Promise<DebuggerShellPreparationResult> {
-    return await unstable_prepareDebuggerShell(
-      process.env.RNDT_DEV === '1' ? 'dev' : 'prebuilt',
-    );
+  async unstable_prepareFuseboxShell(
+    prebuiltBinaryPath?: ?string,
+  ): Promise<DebuggerShellPreparationResult> {
+    return await unstable_prepareDebuggerShell();
   },
 };