These are per camera, so go to go to "cameras" => "alerts", down at bottom click the "on alert" button, for the Action Set page click the "enable" box, down at bottom click on the big "+" sign to add an alert, when popup menu displayd, click on the first one ("Sound"), then select a ".wav" file, at bottom under "Timer", click the radio button for "Loop while camera is triggered", click on OK, then OK, then OK.