Reason 1 :The O2 pressure is low need increase the O2 pressure in the gas tank ;Reason 2 : Decrease the low-pressure value’s pressure let the O2 go through the value but don’t cause the alarm. If the pressure is higher than green indicator no alarm shows .;Reason 3 :Somewhere’s wire connection is broken so we need ingore the alarm then continue to use machine. Select Options then input password “3721”