The FSBS allows fire sprinkler systems to be filled without activating the local waterflow alarm or fire panel. The device consists of a stainless steel double gang faceplate containing a key operated switch assembly to switch between "NORMAL" indicated by a green LED and "BYPASSED" indicated by an amber LED. The FSBS also contains a red LED to indicate if the flowswitch is "ACTIVATED" in either mode. It is designed to mount to a double gang electrical enclosure at least 2"deep.

The red "FLOWSWITCH ACTIVATED" LED provides a visual indication of the flowswitch status in both normal and bypass modes. This helps to prevent unwanted alarms caused by turning the keyswitch back to the ready position while the flowswitch is still activated. It can also be used as a visual indicator to identify which riser is flowing.