Android : how to make android alarm manager work when the apps closed

I work for alarm manager now. i get a good tutorial http://www.techrepublic.com/blog/software-engineer/use-androids-alarmmanager-to-schedule-an-event/

this is my modified code :

public class Main extends Activity implements OnClickListener{
final static private long ONE_SECOND = 1000;
final static private long TWENTY_SECONDS = ONE_SECOND * 20;
final static private long FIVE_SECONDS = ONE_SECOND * 5;
final static private long TEN_SECONDS = ONE_SECOND * 10;

PendingIntent pi;
BroadcastReceiver br;
AlarmManager am;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    setup();
    findViewById(R.id.the_button).setOnClickListener(this);
}

private void setup() {
    br = new BroadcastReceiver() {
        @Override
        public void onReceive(Context c, Intent i) {
            Uri notification = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_ALARM);
            Ringtone r = RingtoneManager.getRingtone(getApplicationContext(), notification);
            r.play();
            Toast.makeText(c, "Rise and Shine!", Toast.LENGTH_LONG).show();
        }
    };
    registerReceiver(br, new IntentFilter("com.authorwjf.wakeywakey") );
    pi = PendingIntent.getBroadcast( this, 0, new Intent("com.authorwjf.wakeywakey"), 0 );
    am = (AlarmManager)(this.getSystemService( Context.ALARM_SERVICE ));
}

@Override
public void onClick(View v) {
    am.set( AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime() + FIVE_SECONDS, pi );
}

@Override
protected void onDestroy() {
    am.cancel(pi);
    unregisterReceiver(br);
    super.onDestroy();
}

}

but i have a problem now, when i close the apps, alarm not works,

How to make this apps still ring alarm when it close or not active?