Fire alarm terms glossary: devices, signals and power
Fire alarm vocabulary comes in families. Once you know which family a word belongs to, you know what questions to ask about it. This glossary groups the terms Level I candidates meet into five families and links each one to a short page with a drawing, a worked example and the mix-ups that cost new technicians points. The terms are explained in our own words, so keep your copy of NFPA 72 (2022) open for the exact requirements.
How to use the glossary
Read a family at a time, not a term at a time. Pick one family, read its table, then open the page for any term you cannot explain out loud in two sentences. Come back to the free check afterward to see whether the gap closed.
Initiating devices: what starts an event
Initiating devices are the field devices that tell the panel something has happened. Some report a possible fire, and others report that a watched system is off normal.
| Term | In one line | Full page |
|---|---|---|
| Photoelectric vs ionization | Two ways a smoke detector senses smoke | Photoelectric vs ionization smoke detector |
| Heat detector | Alarms on temperature, never on smoke | Heat detector |
| Manual pull station | A person starts the alarm by hand | Manual pull station |
| Duct smoke detector | Samples duct air to control fans, not to protect rooms | Duct smoke detector |
| Waterflow switch | Water moving in a sprinkler pipe is an alarm | Waterflow switch |
| Monitor vs control module | Inputs read contacts, outputs switch loads | Monitor module vs control module |
| Two-wire vs four-wire | One pair, or separate power and alarm pairs | Two-wire vs four-wire smoke detector |
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Installation
A supplied module drawing labels COM, NO and NC. The door interface needs a switched contact that is open while the relay is at rest and closes when the relay operates. Which pair matches that instruction?
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Notification: what tells people to act
| Term | In one line | Full page |
|---|---|---|
| NAC | The circuit that powers horns and strobes | NAC circuit |
| Candela rating | How much light a strobe puts out | Candela rating |
| Temporal-3 | Three pulses and a pause means evacuate | Temporal-3 pattern |
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Circuits and pathways: how the wiring behaves
| Term | In one line | Full page |
|---|---|---|
| SLC | The data loop for addressable devices | Signaling line circuit |
| IDC | A conventional zone of contact devices | Initiating device circuit |
| EOL | The resistor that lets the panel supervise the wire | End-of-line resistor |
| Class A vs B | Out and back, or one route out | Class A vs Class B wiring |
| Class X | Out and back, plus short-circuit isolation | Class X pathway |
| Isolator | Cuts one shorted section off the loop | Short-circuit isolator |
| Addressable | Every device has its own address | Addressable fire alarm system |
| Survivability | Keeping a circuit working in a fire | Pathway survivability |
| Cable markings | FPLP, FPLR and NPLFR in the jacket print | FPLP, FPLR, NPLFR |
Signals and panel behavior: what the panel says and does
| Term | In one line | Full page |
|---|---|---|
| Supervisory | A watched condition is off normal | Supervisory signal |
| Trouble | The alarm system itself has a fault | Fire alarm trouble signal |
| Ground fault | A conductor touches ground | Ground fault |
| Acknowledge, silence, reset | Three different panel actions | Acknowledge, silence and reset |
| Latching | Stays on until reset | Latching vs non-latching signal |
| Alarm verification | Confirms a smoke detector before alarming | Alarm verification |
| Remote annunciator | Repeats the panel's status elsewhere | Remote annunciator |
| Central station | Signals leave the building to be answered | Central station monitoring |
Power: what keeps it running
| Term | In one line | Full page |
|---|---|---|
| Secondary power | Batteries that carry standby, then alarm | Secondary power supply |
For the sizing steps, use the battery calculation method and the battery calculator.
Terms that look alike
- NAC and SLC say what a circuit does. Class A, B and X say how it is wired. A loop can be Class A and an NAC can be Class X, so do not infer one from the other. NAC vs SLC circuits sorts this out.
- Supervisory and trouble both are not alarms. Supervisory is about a watched system. Trouble is about the alarm system itself.
- Silence and reset are different. Silence stops the horns. Reset clears the event only once the cause is gone.
- Survivability and class answer different questions. Class is about opens and shorts, and survivability is about fire exposure.
Fire alarm terms on the NICET Level I exam
The vocabulary runs through the whole outline. Installation is 44 to 54% of Level I and Maintenance is 40 to 50%, and most terms above are the objects those tasks act on. Layout and submittals is the smaller remainder, where you read the same terms as symbols and notes. NFPA 72 (2022) Chapters 3 and 10 hold definitions and fundamentals, and the chapter for each family is named on its pages.
Practice it
Drill the device symbols in the fire alarm symbols quiz and the circuit classes in the fire alarm circuit class drill. Size a circuit with the voltage drop calculator and a cable with the wire size calculator. For the cable families, see the fire alarm cable types guide.
Know the vocabulary? Check the rest of Level I
Take the free 10-question check. It's weighted to the Level I outline, scored by domain and needs no signup, so you see whether installation, maintenance or layout costs you the most points. The Level I course gives you full timed practice exams, an explained answer for every question and the section number to look up for each one.
Sources
Show the list
- NFPA 72 (2022), NFPA, Chapters 3, 10, 12, 14, 17, 18, 23 and 26, referenced by number only.
- Fire Alarm Systems Level I content outline, NICET.
Facts checked 25 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.
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