Installed via clip or clamp to indicate positive or negative air flow of fans, CE-compliant FSW800B series is available with reed/magnet contact and comes in NO and NC configurations. Housing measures 1.3 x 0.7 x 0.3 in. and is constructed of black, UL 94HB plastic. When properly installed and connected in series with optical or audible signaling device, bi-directional switch will activate electrical contact if air flow falls below 8.2 fps – either turning the signaling device on or off.