AFM-01NO is an AFM series air flow monitor. It provides simple and alternative way to indicate positive or negative air flow of fans or bowlers. When it is properly installed and connected in series with an optical LED or audible signaling device. A bi-directional switch will activate an electrical contact will make the air flow of the fan falls below 8.2ft/s and turning the signaling device on or off. The AFM monitor can also be attached to an existing plastic grill or guard.