The rule everyone gets backwards

The common belief is that fire alarm panels need a copper phone line and that cellular is a compromise. The code says close to the opposite.

A digital alarm communicator transmitter, the dialer bolted to your fire panel, has always needed two transmission channels. One copper line by itself has never satisfied NFPA 72. Meanwhile a single non-dialer path, such as a properly supervised cellular or IP communicator, is permitted under the performance-based section of the code, provided it reports its own failure within 60 minutes. NFPA 72 is more permissive toward one cellular path than toward one copper line.

What has shifted across editions is what may serve as that second channel for a dialer. That change is the reason your alarm company's advice from a decade ago no longer matches what an inspector will accept.

The 2013 edition is the hinge. That is when a second copper line stopped being a normal design and became a documented last resort. If your building was commissioned before then and nothing has been touched since, the design on file may no longer match the code your inspector is enforcing.

MFVN: the test is the carrier, not the box

The concept that makes any non-copper replacement acceptable is the managed facilities-based voice network, or MFVN. It entered the code in the 2010 edition and now sits at definition 3.3.172 in the 2025 edition.

The 2025 wording is worth reading closely, because one phrase decides most disputes: an MFVN is a physical facilities-based network capable of transmitting real-time signals with formats unchanged, managed, operated and maintained by the regulated communications carrier to ensure service quality and reliability from the subscriber location to the supervising station. The 2010 edition said "the service provider." The 2025 edition says "the regulated communications carrier." That tightening is deliberate.

California's Office of the State Fire Marshal published the clearest checklist any buyer can use, Information Bulletin 25-006, dated July 10, 2025. It opens by naming the problem directly, noting that many vendors claim to offer POTS replacement services meeting the MFVN requirements of NFPA 72. Its test:

The two listings vendors blur together

Ask a vendor "is it UL listed" and you will get a yes. The question is which listing, for which component, because two different things are being certified.

Section 26.6.3.12 is the one to quote back: where a fire alarm transmitter shares on-premises communications equipment, that shared equipment must be listed as communications or information technology equipment. So a UL 864 listing on an adapter does not make the service an MFVN, and a UL 62368 listing does not make the box a fire alarm communicator. Both hurdles have to be cleared, by the right component.

Watch the exact wording in vendor literature. At least one major POTS replacement product describes itself as built with the applicable guidelines of UL 864 and 62368-1, NFPA 72 and ASME A17.1 in mind. Built with guidelines in mind is not a listing. Third-party write-ups of that same product describe it as UL 864 certified, which the manufacturer's own language does not support. Ask for the listing number and the listee name, then check it.

The standby power number is 24 hours

Some jurisdictions go further. The Town of Brighton, New York requires the router or gateway to match the panel's own requirement, either 24 hours or 60 hours. If your replacement box ships with an 8 hour battery and nobody has documented a risk analysis, you have a finding waiting to happen at the next inspection.

Supervision and timing, the numbers that get misquoted

You will still see the 5 minute supervision figure quoted, sometimes by alarm vendors in their own white papers. That number is an artifact of the 2010 edition and was relaxed to 60 minutes in the 2013 edition. If a proposal justifies itself against the 5 minute rule, it is working from a code book that is more than a decade old.

The clean way to keep an old panel

If your fire alarm control unit still works and you simply need it off copper, the code gives you a sanctioned path, and it is not an adapter.

Section 26.6.4.1.1 says the dialer-specific requirements do not apply when the dialer is used as a signaling interface from the fire alarm control unit to another listed communication means, and 26.6.4.1.2 requires that listed means to meet either the performance-based section or the prescriptive radio section. In plain terms: put a properly listed fire alarm communicator in front of the old dialer, and the copper-line rules fall away entirely. The panel keeps talking to a box it understands, and the box handles the outside world on a path the code recognizes.

That is the difference between a compliant design and a hopeful one. A generic adapter is unlisted for this purpose and is treated as shared equipment. A listed communicator is part of the fire alarm system.

New in the 2025 edition: auxiliary service providers

If your replacement routes alarm signals through a vendor's cloud before they reach your monitoring company, the 2025 edition now has a name and a rulebook for that vendor. An auxiliary service provider is an entity that receives signals from the premises, modifies or manipulates them, and passes them on, positioned so that signals cannot reach the supervising station without it. Many cloud-based POTS replacement offerings are exactly this.

• All pathways from premises to provider to supervising station supervised at 60 minutes or less (26.2.11.2.1)
• Pathway failure annunciated at both the supervising station and the provider within 90 seconds (26.2.11.2.2)
• The provider must be approved (26.2.11.2.4)
• The supervising station, building owner and authority having jurisdiction must be notified in writing within 30 calendar days of using or changing one (26.2.11.2.5)
• Signal records retained at least one year (26.2.11.2.6), and facilities conforming to UL 827 (26.2.11.4)

The written notification requirement is the one that catches people. If a vendor inserts themselves into your signal path, somebody owes three parties a letter.

Which edition applies to you

NFPA publishes the code. States and cities adopt it, often years later and with local amendments, so the edition being enforced in your building is a local question with a local answer. Four real examples show how wide the spread is:

Ask your authority having jurisdiction which edition they enforce before you accept any vendor's compliance claim. A product that satisfies the 2025 edition may still need a variance in a town enforcing 2007.

Swapping the path triggers testing, and sometimes a permit

This is not a like-for-like swap you can do quietly on a Friday afternoon.

• Reacceptance testing is required. Section 14.4.1.2 triggers it after any modification, repair or adjustment to system hardware or wiring. Changing the communication path qualifies.
• Specific dialer tests apply. Disconnect the primary line and confirm trouble both on site and at the supervising station within 4 minutes, disconnect the secondary line, and simulate a fault in the primary telephone number.
• Notify before you test. Section 14.2.3.1 requires notifying all affected parties including the monitoring company, and many fire codes require notifying the fire code official first.
• Paperwork varies. New York City requires the FA-12 managed facilities-based voice network certification form at inspection. New Jersey publishes dedicated POTS to MFVN permit paperwork.

Our view

The honest summary is that cellular and IP replacements for fire alarm lines are legitimate, well established, and in some respects better supported by the code than the copper they replace. The risk is not the technology. It is buying a box from someone who cannot answer the question California's fire marshal asks first: who is the carrier of record?

Get that answer in writing, get the listing numbers for both the communicator and the shared equipment, confirm the standby battery against the 24 hour baseline, and confirm which edition of the code your inspector enforces. Four questions. A vendor who can answer all four is selling you something that will pass. One who deflects on any of them is selling you a finding.

For the wider picture on copper retirement, what it costs, and the other lines in your building that need a plan, see the POTS line replacement guide. Elevator phones have their own code and their own trap, covered in the elevator phone POTS replacement guide.

Sources

• NFPA 72-2025, National Fire Alarm and Signaling Code, including the referenced publications list at 2.3.11 and Chapter 26
• NFPA 72-2025 TIA 25-1 (dialer transmission channels) and TIA 25-2 (auxiliary service providers), both issued April 18, 2024
• CAL FIRE Office of the State Fire Marshal, Information Bulletin 25-006, July 10, 2025
• FDNY Technology Management Bulletin 03-2/2012, on managed facilities-based voice networks
• King County, Washington, DACT Interpretation 2015-1
• Town of Brighton, New York, Office of the Fire Marshal bulletin on single path communication
• CableLabs, Managed Facilities-Based Voice Networks and the National Fire Code
• Code editions and local amendments change. Confirm the enforced edition with your authority having jurisdiction before relying on any date or section number here.