Follow directions for adding a chime, beep, tone or any sound file of your choice to the target device as shown in Notes at the top of this thread, test it. Then use the device’s Chime or Beep command using WebCore or Groovy Smartapp.
Should you be using my SmartApp SHM Delay 2.0 there is an option in the Delay profile that does this.
To speak messages of your choice, try using BigTalker 2.0