setAlarm function in MainActivity

public void setAlarm() {
    Intent intent = new Intent(getApplicationContext(), AlarmReceiver.class);
    mSender = PendingIntent.getBroadcast(getApplicationContext(), 0, intent, PendingIntent.FLAG_CANCEL_CURRENT);
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(System.currentTimeMillis());
    calendar.add(Calendar.SECOND, 10);
    AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    alarmManager.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), mSender);
}