AlarmManager

AlarmReceiver.class

public class AlarmReceiver extends BroadcastReceiver
{
    private static int conn_length = -1;
    @Override
    public void onReceive(Context context,Intent intent)
    {
        File directory = new File("/sys/bus/usb/devices");
        File[] contents = directory.listFiles();

        if(contents.length == conn_length){
            return;
        }
        else{
            conn_length = contents.length;
        }

        if(conn_length == 0)
        {

            Toast.makeText(context,"otg not connected",Toast.LENGTH_SHORT).show();
        }
        else
        {
            Toast.makeText(context,"otg connected",Toast.LENGTH_SHORT).show();
        }
    }
}



MainActivity.class

public class MainActivity extends AppCompatActivity
{
    private Process suProcess;
    private PendingIntent pendingIntent;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        getRoot();

        Handler handler = new Handler();
        handler.post(alarmUpdater);
    }

    public Runnable alarmUpdater= new Runnable() {
        @Override
        public void run() {
            startAlarm();
        }
    };

    private void getRoot()
    {
        try
        {
            suProcess = Runtime.getRuntime().exec("su");
        }
        catch (IOException e)
        {

        }
    }

    private void startAlarm()
    {
        Intent alarmIntent = new Intent(MainActivity.this, AlarmReceiver.class);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, alarmIntent, 0);

        AlarmManager manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        int interval = 1000;
        manager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), interval, pendingIntent);
    }
}