mainActivity

private BluetoothAdapter bluetoothAdapter; 
Button  scanButton; 
private static final int REQUEST_ENABLE_BT = 1; 
private ArrayAdapter<String> mNewDevicesArrayAdapter;  
Setup oncreateFirst check if your smartphone supports BluetoothbluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); 
if (bluetoothAdapter == null) { Toast.makeText(this, "Device does not support bluetooth", 
Toast.LENGTH_SHORT).show(); 
finish(); 
} 
else if (!bluetoothAdapter.isEnabled()) { Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); 
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT); 
}