... thealarm give DiDi sound (the ALARM LED flash twice), thewindow display flashing “-“. After approximately 4min itdisplay “0”, and the alarm enter ... not reach pre-set alarm level, the digital display LED display concentration changing by1 ,2 …9. when display 3~9, the STATE LED light ... :When the concentration reach pre-set alarm level, the LED display A, and the unit alarm, STATELED light red and ALARM ...