Using this app with micro controllers (Arduino, Raspberry Pi, AVR, ARM etc), HC-05 Bluetooth Module and Relay Module you can control your home appliances using your smartphone remotely.

Read documentaion : http://unciarobotics.com/project/home-automation-project-with-arduino-using-hc-05/

The basic Arduino code to read data transmitted over Bluetooth is as follows:

const int relay = 2; //pin where Relay is connected
char data; //variable to store data
void setup() {
Serial.begin(9600); //Begin serial communication
pinMode(relay, OUTPUT); //make relay pin as output
}

void loop() {
if (Serial.available() > 0) //if there is data on RX
{
data = Serial.read(); //save it inside variable
if (data == 'a')
{ digitalWrite(relay, HIGH); //Turn ON the Light
Serial.println("Light ON");
}
if (data == 'b')
{ digitalWrite(relay, LOW); //Turn OFF the Light
Serial.println("Light OFF");
}
}
}
}
}

//Copy Paste this code into Arduino IDE and monitor the data on Serial Monitor.