If you check page 44 of the current manual, it explains that this is a user setting. You open the controller and set the alarm for too high only (factory setting), too high and too low or off. This was on different pages in older issues of the manual, but it is there and is present in every osmolator since 2002.
By the way, the too low is triggered by the pump being triggered to run for 10 minutes and a top off not being registered, there is no detection for the pump being dry, etc, it is only a timer.