MediaPLayer not stopping - audio

Question

I dont understand how to actually get this to work. My code is;
package com.example.user.medialert;
import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import java.io.IOException;
/**
* Created by User' on 9/24/2016.
*/
public class alert extends Activity {
final MediaPlayer Siren = new MediaPlayer() ;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.alert);
MediaPlayer Siren = MediaPlayer.create(this, R.raw.alertsiren);
try {
Siren.prepare();
} catch (IOException e) {
e.printStackTrace();
}
Siren.start();
}
public void onClickOk1(View view) {
Siren.stop();
Intent intent = new Intent(alert.this, counter.class);
startActivity(intent);
}
}
The onClick changes the activity as it is supposed to however when I add the Siren.Stop(); code, 'Siren' is invalid, the error being cannot resolve symbol.
I have tried
MediaPlayer Siren = new MediaPlayer();
above the onCreate method, allowing siren to be used in the onClick, but it still doesn't stop playing the sound.
Any ideas?
EDIT
Added to show the code I have updated attempting to make final, and this now crashes the app.
Highlighting Siren under the onCreate method shows that the program isn't linking the Siren in the Siren.stop(); call