How to Meet 520 Hz Multi-Station Smoke Alarm?

7/26/2024

How have people been addressing the IFC (2021) Section 907.5.2.1.3.2 requiring 520Hz single/multiple station smoke alarms in residential units being addressed?

It sounds like there are no 520 Hz smoke alarms available on the on the market meet these requirements. We have a roughly 300-unit building and the AHJ is pushing us to put smoke detectors with sounder bases in each unit instead of 120v smoke alarms.

We know this could be done, but the cost impacts would be substantial and the future maintenance and inspections in the building would be very difficult.

This is the first time we've seen this be pushed by an AHJ, so looking for information on how others have handled this.

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25 Comments

Chad

7/26/2024 08:31:36 am

That’s the only solution right now until they make smoke alarms with LF sounders

Ricardo Gonzales Jr

7/26/2024 08:54:59 am

There are smoke alarms with the 520Hz available. However, they are more expensive than the older version.

Do a cost analysis, battery life, etc and present it to the AHJ. Odds are the AHJ doesn't know and relying on when he/she was an inspector and doesn't keep up with technology.

Chad

7/26/2024 09:00:10 am

Ricardo,

Do you know of a brand or a part number of a 520 Hz smoke alarm? (Not detector)

I haven’t seen one before

Ricardo Gonzales Jr

8/14/2024 09:11:27 am

I saw them at Home Depot, but when I look on-line, they don't show up. I haven't been back in a few weeks. I'll stop there and see if they have them and take pictures.

Jack G

7/26/2024 09:19:26 am

They are not available in my 3 areas that I work in. Online companies that have them on their menu are out of stock.
This new tech stuff should have a 6 month grace period so manufacturers can keep up. In my area, that’s what they do with code changes as plans take a while to develop.

Jay

8/5/2024 02:44:03 pm

The requirement for low frequency square wave audible notification in sleeping areas was first introduced in the 2010 edition of NFPA 72, with an effective date of January 1, 2014. The manufacturers were first given a 3 year window to develop a solution and have now had over 14 years.

Sean

7/26/2024 10:02:01 am

Here was a good article from Jensen Hughes that may be worth sharing with the AHJ or customer. It's from 7 months ago and notes the technology doesn't exist yet, and I've heard that there are outfits trying to develop 120V LF Smoke Alarms, however I am not aware of a product yet. The discussion may go towards justifying the additional cost to include it on the building fire alarm system.

https://www.jensenhughes.com/insights/single-and-multi-station-low-frequency-audible-signaling

Brian

7/26/2024 05:57:42 pm

As a third-party acting as the AHJ for several jurisdictions, we basically have not enforced this requirement. Those that have seem to regret go back to the tried and true design.

Katie

8/15/2024 04:29:55 pm

As a member of the AHJ we have added language (amendment) to Section 907.5.2.1.3.2 to read: shall be a 520-Hz signal complying with NFPA 72 or an alternative means approved by the fire code official. Until technology catches up, we allow the 120v single/multi-station just like in a single-family dwelling. That way we are not just blatantly not enforcing a code we adopted.

Chad

8/15/2024 04:32:53 pm

As an AHJ, I understand and acknowledge that local amendments are necessary evil. We use a few. It’s just unfortunate that the standard has changed so drastically and we’re not all on the same page, Nationally. Many places are enforcing this full throated.

Chad

8/15/2024 04:38:25 pm

I’ve heard that Kidde and BRK have no intention of pursuing the development one of these devices. It’s not practical to run one on a 9 V battery. My fear is the technology will never catch up.

Just the misunderstanding and calls for “false alarms“ will be annoying at best And downright dangerous at worst.

Taylor

1/14/2025 02:49:51 pm

We are attempting a solution that minimizes complexity to the fire alarm system itself.
We are proposing having a secondary smoke only system, ran by a 6820 SK panel and expander cards to accommodate the points. the smoke system would have its own battery backup, completely separate from the FA system that calls out to the monitoring company. This way, the smokes can be activated independently without sending calls out. If there is actually a fire, the sprinklers would activate and the flow would trigger the Fire Department to come. Still trying to figure out exactly how to produce battery calcs, since the whole smoke system wouldn't be active all at the same time. our sounder bases draw 90mA, but really, no more than 4-5 for a 3 bedroom unit should be active at one time. If the fire is large enough to hit multiple units at once, then the main FA system should trigger.

This also allows for installation of multiple 6820's on large campus style projects to reach each section of the building, and using 6815 expanders with 6860 mounting boxes.

If there is a simpler way of accomplishing this, I am all ears.

Ricardo Gonzales Jr

1/14/2025 03:33:22 pm

As the comments above indicate the 520Hz devices require a lot more power to operate. This would be consistent with audio systems where the low frequencies draw more power over the same time frame than higher frequencies. i.e. LF vs. Voice. A 9V smoke alarm would have one activation and then the battery would need replacing. LF is a power hog.

Ethan Borrero

3/19/2025 05:04:32 pm

We too, as an AHJ are experiencing issues finding a 120VAC Low-Frequency Alarm for single & multiple-station smoke alarms in sleeping units of R-1 and R-2 occupancies. Fire alarm systems have not been an issue. Below is an article posed by Jensen Hughes regarding 120VAC Low-Frequency Alarms. Here we are in March of 2025 and the industry still hasn't caught up which is strange.

https://www.jensenhughes.com/insights/single-and-multi-station-low-frequency-audible-signaling

Ricardo Gonzales

5/5/2026 11:44:40 am

When directed to using 520Hz, the companies I worked with went straight to Fire Alarm Systems and avoided Smoke Alarms. Initially, only the major manufacturers had the 520Hz in any form. Later the Residential Fire Alarm Systems carried them via commercial sounders. There has been a lot of talk of smoke alarms having them, but I've not yet seen them in the market.

Jason Lupa, PE link

6/19/2025 01:57:58 pm

The IBC still allows 120VAC single or multiple-station smoke alarms, but they must now produce a 520-Hz signal. Currently there are no 120VAC smoke alarms on the market with an integral 520 Hz sounder. Because of the standby power capacity requirements, they are not cost effective to manufacture.

Satisfying the new codes will necessitate utilizing the building’s fire alarm system:

1. System smoke detectors with low-frequency sounder bases (ABHW-4BS) – preferred for standard units.

2. System smoke detectors with addressable notification or dedicated NACs for each residential unit (SC low frequency appliances supported by HCP or PAD-5) – preferred for ADA/ hearing impaired units requiring audible and visual coverage.

The residential unit system smoke detectors must be programmed as supervisory signals which are non-latching/ self-restoring. This will allow them to automatically deactivate when the smoke condition clears. Voice systems may use one of the above options with the addition of speaker appliances that have a frequency range which includes 520Hz. Select a low-frequency pre-announce tone to be broadcasted before the voice message. Siemens SC high-fidelity speakers have a frequency-response range of 300 to 8000 Hz.

Dan Morehead

10/31/2025 03:59:32 pm

I love this new code as a fire alarm designer and contractor. We are able to utilize the capabilities of the Fire Alarm System to meet this code requirement for all new Multifamily R2 occupancies. We removed the 520-Hz fire alarm "Building Alarm" horns from all the sleeping rooms and replaced them with fire alarm smoke/co detectors and 520-Hz sounder bases. This design actually reduces the "openings" or "wall warts" in each unit. I use the programing features of the fire panel to only activate the sounders in a particular unit as a non-latching, local supervisory signal if the detectors in that unit activate. If a building alarm activates such as waterflow I can activate the sounder bases in all the units. I also have the capability to produce a temporal 3 tone for fire alarm and a temporal 4 tone for C.O. The cost is higher but there are also some cool features. The property manger never has to deal with a tenant removing a detector or battery from a detector ever again. If these detectors are removed they report instantly to the fire panel and identify the unit and even the location within the unit. I hope they never develop a standalone 120VAC detector with 520-Hz.

Chad

10/31/2025 05:42:11 pm

Although I share your sentiment.

Gentex finally made one. And unless you are buying 1000 or more you have to pay retail-

https://fireprotection.gentex.com/products/place-anyspace

Roger

5/5/2026 07:36:51 am

Is there any other manufacturer that Gentex? Our AHJ is enforcing the new UL 217, 10th edition, but Gentex is only certified through the 9th edition. So they're saying we can't use the Gentex until it's UL 217 10th edition certified. Thoughts?

Ricardo Gonzales

5/5/2026 11:20:54 am

I suggest getting a rapport with the AHJ and present the challenge they generated. Solicit their help in finding that equipment they demand via adopted code. More often than not, they don't understand the technical side or challenges they bring to the table.

Wes

5/5/2026 11:25:37 am

Kindly disagree with this sentiment. I'm not an AHJ, but it's not their duty (nor are they allowed to, actually) make a specific design or engineering solution, including making product recommendations.

Often times the person who's representing the AHJ doesn't even have the resources to be an expert in all things that their jurisdiction is involved in.

Can they help collaborate and work through possible acceptable solutions? Of course. Fair to ask what solutions have been acceptable for other/similar projects? Sure. But they're not being paid nor responsible to do design for the design experts, in my opinion.

Chad

5/5/2026 11:34:06 am

I think ricardo was offering an indirect solution to the fact the AHJ does not know you cannot get a 10th edition compliant 120v single/multistation smoke alarm.

you can with system devices

that might be the AHJ's unspoken angle, he wants that, extremely expensive and super annoying, but code compliant solution... and this coming from an AHJ

Or he is just stubborn and wants it

Ricardo Gonzales

5/5/2026 11:34:53 am

Having been an AHJ, they should understand what their Code/Amendment is asking for. At least to the point where a manufacturer is either making the item OR in testing for UL/ERTL or the like. That lack of knowledge could produce a lot of variations of code for the AHJ and they'll have to do the evaluation every time a permit request is submitted until the equipment is commonly available.

Wes

5/5/2026 11:36:09 am

Got it - that makes sense, and I agree. Thanks.

Jason Lupa, PE link

5/5/2026 08:36:00 pm

Hotels, dormitories and apartment buildings now require the use of low frequency alarms for audible notifications activated by either in-unit smoke detection or the building fire alarm system.

Changes to the 2021 edition IBC strive to make use of low frequency signals more consistent throughout all sleeping areas. Group R-1 and R-2 occupancies MUST provide 520-Hz low-frequency notification initiated by:

General building fire alarm notification audible signals – IBC 907.5.2.1.3.1

Local smoke detection notification audible signals - IBC 907.5.2.1.3.2

The code allows for either a 120VAC smoke alarm (UL217) or a 24VDC system smoke detector (UL268) which mimics a smoke alarm. There are limited 120VAC smoke alarms capable of providing the 520 Hz signal and their price-point is 10x the standard versions. Design professionals may want to consider alternative means of compliance, such as UL217 smoke detectors with integral sounder bases, programmed as supervisory signals and self-restoring. They provide a much longer lifecycle and features.

How to Meet 520 Hz Multi-Station Smoke Alarm?

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