Sentinel 703211 Controller The sentinel chhc-4i is the most advanced Co2 controller available on the market today It incorporates the proprietary s.I.C.E. - sentinel intelligent Co2 enrichment - communication and control components and programming that are unique to sentinel It allows for communications between sentinel s.I.C.E series products, providing a level of control never before seen in your greenhouse, garden or grow room The system works by a sentinel s.I.C.E. Series controller, such as the sentinel chhc-4i, measuring and monitoring your growing environment As the atmospheric Co2 levels change, the controller will tell the sentinel ice series generator to increase output, decrease output or go into idle mode...all computer controlled