TrolMaster AS-4 CO2 Alarm Station (Blue Light)TrolMaster AS 4 CO Alarm Station with Blue LED & Digital PPM Display Enhance safety in your grow facility with the TrolMaster AS 4 CO Alarm Station. Designed to be mounted outside your grow room, the AS 4 continuously monitors carbon dioxide (CO) levels using input from either the AL 1 or AL 2 CO sensorsor both for full redundancy. Equipped with a vibrant blue LED indicator, audible alarm, and LCD digital display, this module immediately alerts you if