Exterior Horn/Strobe Alarm or Waterflow Only?

8/5/2025

Can an outside horn and strobe be used for a general alarm, or just for water flow only?

I can't find anything specific in NFPA 72, 2016 edition.

Is it more of an AHJ call?

I can understand where it could be a nuisance if used for general alarm notification.

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6 Comments

Glenn Berger

8/5/2025 08:05:20 am

The question asked "CAN an ...." - to this the answer is YES.

Casey Milhorn

8/5/2025 08:14:29 am

Many of the AHJs around us prefer, or even require, horn/strobe combos for waterflow. Having the visual signal can be very helpful to identify where the sound is coming from. This is almost a necessity when you get into an area where multiple automatic sprinkler risers are located in close proximity and sound may bounce from adjacent walls. It can be difficult to tell which riser is in flow condition without the strobe.

Jake Powell

8/5/2025 08:17:32 am

Look at 6.8.1 of NFPA 13 (2016) and 17.12 of NFPA 72 (2016). We require the exterior H/S above the FDC to be programmed to only activate on waterflow, not general alarm. This H/S is on a separate NAC that is programmed to be non-silenceable to meet 6.8.1

Jon N.

8/5/2025 09:39:13 am

The original intent of an outside fire sprinkler flow alarm (in those days, often a water motor gong), was to produce an audible alarm so that neighbors or passersby would call the fire department. This was years before automatic fire alarm systems (and sprinkler monitoring) became common in buildings.

The role of these devices has changed (in my opinion). Relatively few fire sprinkler water flow responses are generated from a neighbor or passerby. Far more are generated from monitored fire alarm systems via central stations, remote stations, or proprietary stations.

As a former AHJ concerned with prompt responses to sprinkler activations and water flow, the desire was to have a horn / light combination (not necessarily a horn / strobe unit) located above the fire department connection. Flashing lights capture the attention of responding fire companies who often cannot hear the audible alarm over the sound of their engine.

By placing the horn / light unit near the FDC, if helps responding firefighters know where that device is located,

Personally, I've never been a big fan of exterior alarm devices that are not part of the fire sprinkler system. It can cause confusion for firefighters who may think there is a sprinkler system in the building.

Some older codes required an outside audible device for school fire alarm systems. I believe that was a throwback to the Our Lady of Angels School fire in 1958 where the initial notification was from a street fire alarm pull box a block or so away.

Mark C.

8/5/2025 11:53:34 am

I am an AHJ and many municipalities use exterior A/V for general fire alarm in multi-tenant occupancies and/or strip malls. We require a blue exterior strobe located above the FDC for water-flow, but a clear (or white) strobe in these applications to indicate smoke detector activation within a specific unit or area in multi-tenant spaces to help responding units to identify a more specific location of the activation.

In the multi-tenant buildings or strip malls, we require either individual flow switches for each separate space or full automatic smoke detection for addressibility. The flow switch, pull station, or detectors within the individual space is programmed to send the specific address of the unit and activates the clear strobe by the Knox Box and main entrance of the individual space, where an annunciator panel is located. The main flow switch in the riser room, if activated, would activate the blue strobe above the FDC.

I guess in short, my answer to your question is yes, exterior strobes can be used for general alarm, but I wanted to give you a more detailed explaination to how we do it.

Jack G

10/4/2025 09:17:23 pm

Agree with mark C, and like the idea if a strobe above the fdc. I ve only run into it in a few townships but think it should go into the building codes.

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Exterior Horn/Strobe Alarm or Waterflow Only?

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