diff --git a/usbserial/src/main/java/com/felhr/usbserial/CDCSerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/CDCSerialDevice.java
index 717fd8e..970e87a 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/CDCSerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/CDCSerialDevice.java
@@ -93,10 +93,12 @@ public class CDCSerialDevice extends UsbSerialDevice
             setThreadsParams(requestIN, outEndpoint);
 
             asyncMode = true;
+            isOpen = true;
 
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -109,6 +111,7 @@ public class CDCSerialDevice extends UsbSerialDevice
         killWriteThread();
         connection.releaseInterface(mInterface);
         connection.close();
+        isOpen = false;
     }
 
     @Override
@@ -119,6 +122,7 @@ public class CDCSerialDevice extends UsbSerialDevice
         {
             setSyncParams(inEndpoint, outEndpoint);
             asyncMode = false;
+            isOpen = true;
 
             // Init Streams
             inputStream = new SerialInputStream(this);
@@ -127,6 +131,7 @@ public class CDCSerialDevice extends UsbSerialDevice
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -137,6 +142,7 @@ public class CDCSerialDevice extends UsbSerialDevice
         setControlCommand(CDC_SET_CONTROL_LINE_STATE, CDC_CONTROL_LINE_OFF, null);
         connection.releaseInterface(mInterface);
         connection.close();
+        isOpen = false;
     }
 
     @Override
diff --git a/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java
index 2792165..70deb4d 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/CH34xSerialDevice.java
@@ -130,10 +130,12 @@ public class CH34xSerialDevice extends UsbSerialDevice
             setThreadsParams(requestIN, outEndpoint);
 
             asyncMode = true;
+            isOpen = true;
 
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -145,6 +147,7 @@ public class CH34xSerialDevice extends UsbSerialDevice
         killWriteThread();
         stopFlowControlThread();
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
@@ -157,6 +160,7 @@ public class CH34xSerialDevice extends UsbSerialDevice
             createFlowControlThread();
             setSyncParams(inEndpoint, outEndpoint);
             asyncMode = false;
+            isOpen = true;
 
             // Init Streams
             inputStream = new SerialInputStream(this);
@@ -165,6 +169,7 @@ public class CH34xSerialDevice extends UsbSerialDevice
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -174,6 +179,7 @@ public class CH34xSerialDevice extends UsbSerialDevice
     {
         stopFlowControlThread();
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
diff --git a/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java
index d442d9e..e24b4f5 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/CP2102SerialDevice.java
@@ -116,10 +116,12 @@ public class CP2102SerialDevice extends UsbSerialDevice
             setThreadsParams(requestIN, outEndpoint);
 
             asyncMode = true;
+            isOpen = true;
 
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -132,6 +134,7 @@ public class CP2102SerialDevice extends UsbSerialDevice
         killWriteThread();
         stopFlowControlThread();
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
@@ -144,6 +147,7 @@ public class CP2102SerialDevice extends UsbSerialDevice
             createFlowControlThread();
             setSyncParams(inEndpoint, outEndpoint);
             asyncMode = false;
+            isOpen = true;
 
             // Init Streams
             inputStream = new SerialInputStream(this);
@@ -152,6 +156,7 @@ public class CP2102SerialDevice extends UsbSerialDevice
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -162,6 +167,7 @@ public class CP2102SerialDevice extends UsbSerialDevice
         setControlCommand(CP210x_IFC_ENABLE, CP210x_UART_DISABLE, null);
         stopFlowControlThread();
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
diff --git a/usbserial/src/main/java/com/felhr/usbserial/FTDISerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/FTDISerialDevice.java
index 8f7f1a4..c3aa277 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/FTDISerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/FTDISerialDevice.java
@@ -126,10 +126,12 @@ public class FTDISerialDevice extends UsbSerialDevice
             setThreadsParams(requestIN, outEndpoint);
 
             asyncMode = true;
+            isOpen = true;
 
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -143,6 +145,7 @@ public class FTDISerialDevice extends UsbSerialDevice
         killWorkingThread();
         killWriteThread();
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
@@ -158,9 +161,12 @@ public class FTDISerialDevice extends UsbSerialDevice
             inputStream = new SerialInputStream(this);
             outputStream = new SerialOutputStream(this);
 
+            isOpen = true;
+
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -172,6 +178,7 @@ public class FTDISerialDevice extends UsbSerialDevice
         setControlCommand(FTDI_SIO_MODEM_CTRL, FTDI_SET_MODEM_CTRL_DEFAULT4, 0, null);
         currentSioSetData = 0x0000;
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
diff --git a/usbserial/src/main/java/com/felhr/usbserial/PL2303SerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/PL2303SerialDevice.java
index 0ba47b4..5754777 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/PL2303SerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/PL2303SerialDevice.java
@@ -73,10 +73,12 @@ public class PL2303SerialDevice extends UsbSerialDevice
             setThreadsParams(requestIN, outEndpoint);
 
             asyncMode = true;
+            isOpen = true;
 
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -87,6 +89,7 @@ public class PL2303SerialDevice extends UsbSerialDevice
         killWorkingThread();
         killWriteThread();
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
@@ -97,6 +100,7 @@ public class PL2303SerialDevice extends UsbSerialDevice
         {
             setSyncParams(inEndpoint, outEndpoint);
             asyncMode = false;
+            isOpen = true;
 
             // Init Streams
             inputStream = new SerialInputStream(this);
@@ -105,6 +109,7 @@ public class PL2303SerialDevice extends UsbSerialDevice
             return true;
         }else
         {
+            isOpen = false;
             return false;
         }
     }
@@ -113,6 +118,7 @@ public class PL2303SerialDevice extends UsbSerialDevice
     public void syncClose()
     {
         connection.releaseInterface(mInterface);
+        isOpen = false;
     }
 
     @Override
diff --git a/usbserial/src/main/java/com/felhr/usbserial/UsbSerialDevice.java b/usbserial/src/main/java/com/felhr/usbserial/UsbSerialDevice.java
index 2ab7fbe..90dddeb 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/UsbSerialDevice.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/UsbSerialDevice.java
@@ -40,6 +40,8 @@ public abstract class UsbSerialDevice implements UsbSerialInterface
 
     protected boolean asyncMode;
 
+    protected boolean isOpen;
+
     // Get Android version if version < 4.3 It is not going to be asynchronous read operations
     static
     {
@@ -233,6 +235,10 @@ public abstract class UsbSerialDevice implements UsbSerialInterface
             serialBuffer.debug(value);
     }
 
+    public boolean isOpen(){
+        return isOpen;
+    }
+
     private boolean isFTDIDevice()
     {
         return (this instanceof FTDISerialDevice);