AlarmManager doesn`t start BroadcastReceiver

I am trying to use BroadcastReceiver and AlarmManager to set a one-shot alarm. I have no idea why isn`t it working. What am I doing wrong? I have no exceptions, no logs about, no suggestions from IDE, everything seems fine, but onReceive method in my BroadcastReceiver is never called.

    public void setAlarm(Context mContext) {
    AlarmManager alarmManager = (AlarmManager) mContext.getSystemService(Context.ALARM_SERVICE);

    Intent intent = new Intent(mContext, AlarmReceiver.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(mContext, 505151550 ,intent, PendingIntent.FLAG_UPDATE_CURRENT);

    Calendar cal = Calendar.getInstance();
    cal.add(Calendar.SECOND, 20);

    alarmManager.set(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), pendingIntent);
    Log.d("alarm",cal.getTime().toString());
}

I am calling it from the activity:

new MyManager().setAlarm(this);

but I have also tried: new MyManager().setAlarm(MyActivity.this);

public class AlarmReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
    Log.d("alarm","got into alarm receiver");
}}

in AndroidManifest.xml :

<receiver android:name="com.example.AlarmReceiver"></receiver>

but I have also tried

<receiver android:name=".AlarmReceiver"></receiver>

try like this: it will fire alarm after 30 second.

public class TestAlarmManager extends Activity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setAlarm(getApplicationContext());

    }
    public void setAlarm(Context mContext) {

        Intent intent = new Intent(this, AlarmReceiver.class);  
        PendingIntent pendingIntent = PendingIntent.getBroadcast(  
                                      this.getApplicationContext(), 234324243, intent, 0);  
        AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);  
        alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()  
                                      + (30 * 1000), pendingIntent);  
        Toast.makeText(this, "Alarm set in " + 30 + " seconds",Toast.LENGTH_LONG).show();  
    }

}

AlarmReceiver.java

public class AlarmReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent arg1) {
        Log.e("alarm","got into alarm receiver");
        Toast.makeText(context, "Alarm Started..", Toast.LENGTH_LONG).show();  
    }

}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.think.androidteststackoverflow"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher_3"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.think.androidteststackoverflow.TestAlarmManager"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

          <receiver android:name=".AlarmReceiver"></receiver>
    </application>

</manifest>