diff --git a/src/__tests__/unit/lib/transport/WebSocketTransport.lifecycle.test.ts b/src/__tests__/unit/lib/transport/WebSocketTransport.lifecycle.test.ts
index 78f1afc..6317dcd 100644
--- a/src/__tests__/unit/lib/transport/WebSocketTransport.lifecycle.test.ts
+++ b/src/__tests__/unit/lib/transport/WebSocketTransport.lifecycle.test.ts
@@ -799,4 +799,207 @@ describe("WebSocketTransport lifecycle", () => {
       transport.destroy();
     });
   });
+
+  describe("stale WebSocket cleanup", () => {
+    it("should null old WebSocket handlers when createWebSocket creates a new instance", () => {
+      const transport = new WebSocketTransport({
+        deviceId: "test-device",
+        url: "ws://localhost:7497",
+        reconnectInterval: 100,
+      });
+
+      transport.connect();
+      const ws1 = MockWebSocket.getLatest()!;
+      ws1.simulateOpen();
+
+      // Disconnect to trigger reconnect
+      ws1.simulateClose();
+
+      // Wait for reconnect to create a new WebSocket
+      vi.advanceTimersByTime(100);
+
+      const ws2 = MockWebSocket.getLatest()!;
+      expect(ws2).not.toBe(ws1);
+
+      // Old WebSocket handlers should be nulled
+      expect(ws1.onopen).toBeNull();
+      expect(ws1.onclose).toBeNull();
+      expect(ws1.onerror).toBeNull();
+      expect(ws1.onmessage).toBeNull();
+
+      transport.destroy();
+    });
+
+    it("should not create parallel WebSockets from repeated reconnection failures", () => {
+      const transport = new WebSocketTransport({
+        deviceId: "test-device",
+        url: "ws://localhost:7497",
+        reconnectInterval: 100,
+      });
+
+      transport.connect();
+      const ws1 = MockWebSocket.getLatest()!;
+      ws1.simulateOpen();
+
+      // Simulate connection drop
+      ws1.simulateClose();
+
+      // Each reconnect attempt should only create one new WebSocket
+      for (let i = 0; i < 5; i++) {
+        vi.advanceTimersByTime(100);
+        const ws = MockWebSocket.getLatest()!;
+        // Fail the connection
+        ws.simulateClose();
+      }
+
+      // initial(1) + 5 created in loop iterations = 6 total
+      // The key assertion: no parallel WebSockets from duplicate timers
+      // Each iteration should create exactly one new WebSocket
+      expect(MockWebSocket.instances.length).toBe(6);
+
+      // All old instances should have nulled handlers
+      for (let i = 0; i < MockWebSocket.instances.length - 1; i++) {
+        expect(MockWebSocket.instances[i]!.onopen).toBeNull();
+        expect(MockWebSocket.instances[i]!.onclose).toBeNull();
+      }
+
+      transport.destroy();
+    });
+  });
+
+  describe("pauseHeartbeat and reconnection", () => {
+    it("should clear reconnectTimer when pauseHeartbeat is called", () => {
+      const transport = new WebSocketTransport({
+        deviceId: "test-device",
+        url: "ws://localhost:7497",
+        reconnectInterval: 2000,
+      });
+
+      transport.connect();
+      const ws = MockWebSocket.getLatest()!;
+      ws.simulateOpen();
+
+      // Disconnect - this schedules a reconnect timer
+      ws.simulateClose();
+      expect(transport.state).toBe("reconnecting");
+
+      const instancesAfterClose = MockWebSocket.instances.length;
+
+      // Pause heartbeat (app goes to background) - should clear reconnect timer
+      transport.pauseHeartbeat();
+
+      // Advance past the reconnect interval
+      vi.advanceTimersByTime(3000);
+
+      // No new WebSocket should have been created
+      expect(MockWebSocket.instances.length).toBe(instancesAfterClose);
+
+      transport.destroy();
+    });
+
+    it("should block scheduleReconnect when heartbeatPaused is true", () => {
+      const transport = new WebSocketTransport({
+        deviceId: "test-device",
+        url: "ws://localhost:7497",
+        reconnectInterval: 100,
+      });
+
+      transport.connect();
+      const ws = MockWebSocket.getLatest()!;
+      ws.simulateOpen();
+
+      // Pause heartbeat first (simulating app going to background)
+      transport.pauseHeartbeat();
+
+      const instancesBeforeClose = MockWebSocket.instances.length;
+
+      // Now the WebSocket dies while paused
+      // Manually trigger onclose (simulating network drop in background)
+      ws.simulateClose();
+
+      // Advance time well past reconnect interval
+      vi.advanceTimersByTime(1000);
+
+      // No new WebSocket should have been created because heartbeat is paused
+      expect(MockWebSocket.instances.length).toBe(instancesBeforeClose);
+
+      transport.destroy();
+    });
+
+    it("should reconnect successfully after pause, WS death, and resume", () => {
+      const transport = new WebSocketTransport({
+        deviceId: "test-device",
+        url: "ws://localhost:7497",
+        reconnectInterval: 100,
+      });
+
+      transport.connect();
+      const ws1 = MockWebSocket.getLatest()!;
+      ws1.simulateOpen();
+      expect(transport.state).toBe("connected");
+
+      // App goes to background
+      transport.pauseHeartbeat();
+
+      // WebSocket dies while backgrounded
+      ws1.simulateClose();
+
+      // Advance time - no reconnection should happen
+      vi.advanceTimersByTime(500);
+      const instancesWhilePaused = MockWebSocket.instances.length;
+      expect(instancesWhilePaused).toBe(1); // Still just the original
+
+      // App comes to foreground - immediateReconnect triggers
+      transport.immediateReconnect();
+
+      // Advance past the 500ms delay
+      vi.advanceTimersByTime(500);
+
+      // Should have created a new WebSocket
+      expect(MockWebSocket.instances.length).toBe(2);
+
+      // New connection succeeds
+      const ws2 = MockWebSocket.getLatest()!;
+      ws2.simulateOpen();
+      expect(transport.state).toBe("connected");
+
+      transport.destroy();
+    });
+  });
+
+  describe("pong timeout", () => {
+    it("should not create duplicate reconnections from pong timeout", () => {
+      const transport = new WebSocketTransport({
+        deviceId: "test-device",
+        url: "ws://localhost:7497",
+        pingInterval: 1000,
+        pongTimeout: 500,
+        reconnectInterval: 100,
+      });
+
+      transport.connect();
+      const ws1 = MockWebSocket.getLatest()!;
+      ws1.simulateOpen();
+
+      // Trigger ping
+      vi.advanceTimersByTime(1000);
+      expect(ws1.sentMessages).toContain("ping");
+
+      // Let pong timeout fire (closes WS and triggers handleDisconnection)
+      vi.advanceTimersByTime(500);
+
+      // Old WS handlers should be nulled (closeWebSocket was called)
+      expect(ws1.onclose).toBeNull();
+      expect(ws1.onopen).toBeNull();
+
+      // Wait for reconnect
+      vi.advanceTimersByTime(100);
+
+      // Should have exactly 2 WebSocket instances (original + 1 reconnect)
+      // Not 3 (which would happen if onclose also triggered a separate reconnection)
+      expect(MockWebSocket.instances.length).toBe(2);
+
+      transport.destroy();
+    });
+  });
 });
diff --git a/src/lib/transport/WebSocketTransport.ts b/src/lib/transport/WebSocketTransport.ts
index d268d57..ba577ec 100644
--- a/src/lib/transport/WebSocketTransport.ts
+++ b/src/lib/transport/WebSocketTransport.ts
@@ -188,7 +188,12 @@ export class WebSocketTransport implements Transport {
     this.heartbeatPaused = true;
     this.heartReset();
 
-    // Cancel any pending immediate reconnect to prevent connections opening in background
+    // Cancel any pending reconnect timers to prevent connections opening in background
+    if (this.reconnectTimer) {
+      clearTimeout(this.reconnectTimer);
+      this.reconnectTimer = undefined;
+    }
+
     if (this.immediateReconnectTimer) {
       clearTimeout(this.immediateReconnectTimer);
       this.immediateReconnectTimer = undefined;
@@ -215,7 +220,26 @@ export class WebSocketTransport implements Transport {
     }
   }
 
+  private closeWebSocket(): void {
+    if (this.ws) {
+      this.ws.onopen = null;
+      this.ws.onclose = null;
+      this.ws.onerror = null;
+      this.ws.onmessage = null;
+      if (
+        this.ws.readyState === WebSocket.OPEN ||
+        this.ws.readyState === WebSocket.CONNECTING
+      ) {
+        this.ws.close();
+      }
+      this.ws = null;
+    }
+  }
+
   private createWebSocket(): void {
+    // Close any existing WebSocket to prevent stale handlers from corrupting state
+    this.closeWebSocket();
+
     try {
       this.ws = new WebSocket(this.config.url);
       this.setupEventHandlers();
@@ -311,6 +335,11 @@ export class WebSocketTransport implements Transport {
   }
 
   private scheduleReconnect(): void {
+    // Don't schedule reconnects while heartbeat is paused (app backgrounded)
+    if (this.heartbeatPaused) {
+      return;
+    }
+
     if (
       this.isDestroyed ||
       this.reconnectAttempts >= this.config.maxReconnectAttempts
@@ -388,10 +417,9 @@ export class WebSocketTransport implements Transport {
             logger.warn(
               `[Transport:${this.deviceId}] Pong timeout - forcing disconnect`,
             );
-            // Close the WebSocket
-            this.ws?.close();
-            // Force disconnect handling immediately, don't wait for onclose event
-            // This ensures we detect dead connections even if browser doesn't fire onclose
+            // Close and null handlers before triggering disconnect to prevent
+            // onclose from firing a duplicate handleDisconnection()
+            this.closeWebSocket();
             this.stopHeartbeat();
             this.handleDisconnection();
           }, this.config.pongTimeout);
@@ -451,19 +479,6 @@ export class WebSocketTransport implements Transport {
       this.immediateReconnectTimer = undefined;
     }
 
-    if (this.ws) {
-      this.ws.onopen = null;
-      this.ws.onclose = null;
-      this.ws.onerror = null;
-      this.ws.onmessage = null;
-
-      if (
-        this.ws.readyState === WebSocket.OPEN ||
-        this.ws.readyState === WebSocket.CONNECTING
-      ) {
-        this.ws.close();
-      }
-      this.ws = null;
-    }
+    this.closeWebSocket();
   }
 }