The green LED indicator shows the CO2 level is below 800ppm which means the room is safe to entry. The yellow LED indicator shows CO2 level equal or above 800ppm which means supplemental CO2 is in use. The AS-2 will sounds an audible alarm and blinking red LED indicator in the event of the CO2 level going above normal or safe levels.
Please Note: The AS-2 requires the SPH-1 for supplemental power.