Basic Bluetooth communication with Arduino & HC-05

// We will receive from pin 10 and transmit to pin 11
const int BTRX = 10;
const int BTTX = 11;

// Output LED at pin 13
const int LED  = 13;

// We will use this variable to keep track of the status
int val = 0;

// We use software serial to avoid conflicts
// with the default RX/TX pins of the Arduino board
#include <SoftwareSerial.h>
SoftwareSerial SerialBT(BTRX, BTTX);

// Define the message
String msg; 

// Setup the connection
void setup() {
  SerialBT.begin(9600);
  SerialBT.println("Bluetooth connection is established");
  pinMode(LED, OUTPUT);
}

//    Loop waiting for a message in every iteration
//    Analyze message,
//    Trigger action (LED on / off / check status)

void loop() {
  if (SerialBT.available()){      // Data are pending
     msg = SerialBT.readString(); // Read the message
     if (msg == "on") {
         digitalWrite(LED, HIGH);
         SerialBT.print("LED at Pin ");
         SerialBT.print(LED);
         SerialBT.println(" is ON");
      } 
      else
      if (msg == "off") {
         digitalWrite(LED, LOW);
         SerialBT.print("LED at Pin ");
         SerialBT.print(LED);
         SerialBT.println(" is OFF");
      }
      else
      if (msg == "status") {
        val = digitalRead(LED);
        SerialBT.print("LED at Pin ");
        SerialBT.print(LED);
        SerialBT.println(" is ");
        if (val == 0) {
          SerialBT.println("OFF");
        } else {
          SerialBT.println("ON");
        }
      }
      else {
         SerialBT.print("Command <");
         SerialBT.print(msg);
         SerialBT.println("> is unknown");
      }
    }
}