Fire Alarm Communicator
DACT, IP, and Cellular Transmission

What the Communicator Does

The fire alarm communicator (sometimes called a transmitter or off-premises signaling unit) is the device that relays every alarm, supervisory, and trouble signal from your FACP to a remote supervising station. Without a working communicator, the best-designed fire alarm system in the world has no way to get help dispatched. Everything the panel does in-building — horns, strobes, elevator recall, HVAC shutdown — is irrelevant if the fire department never learns a fire has started.

NFPA 72 §26 governs supervising station alarm systems end-to-end. The communicator is part of the transmitter portion of that architecture; the receiver lives at the central station and is a listed UL 1610 device. The signal path between them is what NFPA 72 §26.6 calls the transmission method, and today there are three legitimate choices: dial-up (POTS DACT), network (IP), and cellular.

The Three Transmission Methods

1. POTS DACT (Digital Alarm Communicator Transmitter)

The legacy method, once ubiquitous. A DACT is wired to two dedicated telephone lines and dials out when a signal needs to be transmitted. NFPA 72 §26.6.3.1 requires two separate telephone lines, each tested at least every 6 hours, and the panel must generate a trouble signal if either line fails. The most common example you will see in the field is the Silent Knight 5104B, which appears on the Northside Duluth Outpatient Center report (Model #5104B, Digital Communicator).

DACTs are being phased out because telephone carriers are sunsetting the copper analog infrastructure they rely on. Even where POTS is nominally available, many building owners find the carrier has quietly migrated them to a VoIP or "managed voice" service, which does not meet NFPA 72 supervision requirements. The symptom is persistent phone-line trouble signals that cannot be cleared.

2. IP (Ethernet / Managed Network)

IP communicators transmit alarm data over the building's existing network to a UL-listed supervising station receiver. The advantage is that the path is continuously supervised — the communicator polls the receiver (or the receiver polls the communicator) at an interval short enough that a cut cable generates a trouble signal within minutes instead of hours. NFPA 72 §26.6.4 permits IP as the sole path when the supervision polling interval is 200 seconds or less.

Common examples: Bosch B426-M, DMP 263-IP, Honeywell NetVanta, Teldat MX-IP, Fire-Lite IPDACT-2UD. The unit typically has an RJ-45 port, a local status LED array, and a small web interface for configuration. IP has two weaknesses to plan around: local power loss (the communicator needs its own battery backup on the same schedule as the FACP) and switch/router dependencies (if the edge switch is not on the FACP's backup power, the IP path goes down in a power outage).

3. Cellular (LTE / 5G Radio)

A cellular communicator uses an embedded LTE or 5G modem to transmit signals over the public carrier network — AT&T, Verizon, or T-Mobile depending on the unit. Cellular is the most common backup path in a dual-path deployment, and for single-path installations it is often the only option in buildings without reliable IP. NFPA 72 §26.6.5 governs one-way radio transmission methods, including cellular.

The main variables you manage with cellular: signal strength (measured in dBm; better than −100 dBm is generally safe, −110 dBm and worse becomes marginal), carrier generation (most units shipping in 2026 are LTE; 3G sunset completed in 2022, and carriers are actively retiring 2G), and external antenna (required in basements, metal-clad rooms, and buildings with dense concrete construction). Common cellular units: DMP 263LTE-V, Bosch B450-M, Honeywell IPGSM-4G, Telguard TG-7LA-VZ.

Dual Path — What It Means and When It's Required

A dual-path communicator uses two independent transmission methods simultaneously — most commonly IP as the primary and cellular as the backup, though IP + IP (two carriers) and cellular + cellular (two carriers) are also listed configurations. NFPA 72 §26.6.3 sets the framework: the system must be designed so that any single failure in one path does not prevent signal transmission over the other, and at least one path must be supervised such that a failure is detected within 60 minutes.

Dual path is not explicitly required in the base NFPA 72 text for every occupancy, but it is the practical standard because:

• Insurance carriers increasingly require it for commercial property policies.
• Healthcare facilities under CMS 42 CFR §482.41 effectively need dual path because any loss of fire alarm communication triggers an ILSM assessment and potential fire watch.
• High-rise and assembly occupancies under IBC §907 are often pushed by AHJs to use dual path.
• POTS retirement means single-path DACT is no longer a reliable long-term plan.

If you inherit a building with a single-path DACT on POTS, put dual-path replacement in the capital plan within 12 months. The risk of a silent line failure during an actual fire is not hypothetical — multiple post-incident reports from NIOSH and fire-marshal case files cite dead phone lines as a contributing factor in life-loss fires.

Central Station — Where the Signal Lands

The supervising station (commonly called a “central station”) is a 24/7 staffed facility that receives the transmitted signals and dispatches fire, EMS, or police per your pre-configured account instructions. The station itself must be listed to UL 827 (for UL-listed central stations), FM 3011 (for FM-approved), or equivalent. The receiving equipment inside the station is listed to UL 1610.

When an alarm arrives, NFPA 72 §26.5.1 requires the station to acknowledge and initiate dispatch within 90 seconds. The operator typically calls a pre-designated keyholder and the responding fire department. Supervisory and trouble signals have longer allowable response times (typically 4 and 24 hours respectively) and follow a different escalation path — usually a call to the building contact, not the fire department.

Common supervising stations in the United States: Security Central (Statesville, NC — used by Northside Duluth), Rapid Response (Syracuse, NY), COPS Monitoring (Williamstown, NJ), Affiliated Monitoring (Union, NJ), Vector Security (Pittsburgh, PA). Accounts are typically priced monthly per signal path.

ITM Requirements

NFPA 72 Table 14.4.5 prescribes the testing schedule. Common line items:

• Monthly — test of DACT transmission over both phone lines. Initiate a manual test signal from the FACP; verify the central station logs the event with correct account and zone identifiers.
• Quarterly — functional test of supervised IP and cellular paths. Generate test signals over each path independently and verify receipt.
• Annually — full functional test including signal path diagnostics, battery load test on the communicator, and review of the central station's 12-month signal log for missed tests or unexplained trouble events.
• After any change — retest the full path end-to-end whenever the building changes phone carrier, internet provider, cellular plan, or account identifier with the central station.

Common Field Issues

• Phone-line trouble. Carrier migrated to VoIP without notice; DACT generates continuous Line 1 / Line 2 trouble. Solution: upgrade to IP or cellular dual-path communicator.
• IP path loss on UPS failure. Edge switch is not on FACP backup power; building power blip takes the IP path down for 30 minutes until the switch reboots. Solution: put the switch on the FACP dedicated branch circuit and verify standby battery sizing includes the switch load.
• Weak cellular signal. Communicator is buried in a basement electrical room with −115 dBm signal. Solution: external roof antenna with proper surge protection, or supplemental Wi-Fi calling / femtocell if carrier supports it.
• Wrong account ID transmitted. Technician installed the communicator but used the previous tenant's account number. Solution: end-to-end test after every communicator replacement with the central station operator on the phone.
• Silenced trouble. Operator silenced a communicator trouble months ago and nobody followed up. Solution: any communicator trouble over 4 hours triggers ILSM and fire watch consideration.

Frequently Asked Questions

References