Android snippet for hiding debug screens behind SECRET_CODE broadcasts sent via the dialler.

AndroidManifest.xml

<receiver android:name=".SecretCodeReceiver">
  <intent-filter>
    <action android:name="android.provider.Telephony.SECRET_CODE" />
    <data
      android:scheme="android_secret_code"
      android:host="1111" />
  </intent-filter>
</receiver>

SecretCodeReceiver.java

public class SecretCodeReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Intent i = new Intent(context, SecretActivity.class);
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(i);
    }
}