wl.acquire();

package com.alarm.alarm;

import android.app.Activity;
import android.os.Bundle;
import android.content.Context;
import android.os.PowerManager;


public class Alarm extends Activity {
    //Context mContext;
	/** Called when the activity is first created. */
	    @Override
	    
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //App "dauer aktiv"
        PowerManager pm = (PowerManager)getSystemService(Context.POWER_SERVICE);
        PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK,
				"Alarm");
        wl.acquire();
        //restlicher Code
     }
}

.setKeepScreenOn( true );