A fire alarm input/output module (I/O module), one type of fire alarm interface module, is an addressable loop device that monitors a volt-free contact from other equipment (the input) and switches a relay to control other equipment (the output). It is how the panel recalls lifts, stops air handling units, releases door locks and reports fire pump controller signals. Model selection starts with the load and the relay contact rating, not the price.
This guide is for contractors and MEP engineers who quantify and specify interface modules. It compares the Context Plus units AZEIDK supplies, including the SA4700-102IMC input/output unit with isolator, with the Bosch AVENAR IO module 4000, and covers placement, relay ratings and how to count modules from the cause and effect matrix.
Key takeaways
- Each control output in the cause and effect matrix usually needs its own output, and each signal from another system needs a monitored input.
- The SA4700-102IMC and SA4700-104IMC relays are rated 1 A at 30 V AC or DC per the datasheet: they are for low-voltage control signals, not 230 V loads.
- For mains loads, the SA4700-103IMC provides a volt-free changeover relay rated 250 V AC at up to 5 A.
- NFPA 72 requires the interface device to be close to the controlled component. The permitted distance depends on the edition and wiring method.
- Context Plus modules run on Context Plus loops; Bosch AVENAR modules run on LSN loops of AVENAR panels. Do not mix them.
In this article
- What is an input/output module in a fire alarm system?
- I/O module or switch monitor?
- Control module vs monitor module in a fire alarm system
- Fire alarm input/output module types: single, twin or mains switching?
- Which module for which equipment?
- Where to install, wire and supervise the module
- Isolator module and smoke detector with isolator base: when do you need them?
- Fire alarm control module wiring diagram and PDF datasheets
- How many I/O modules to order: counting from the cause and effect matrix
- How are I/O modules tested at handover?
- Common mistakes
- FAQ
- Conclusion
What is an input/output module in a fire alarm system?
On an addressable loop every device has an address the panel reads. A detector reports smoke or heat. An I/O module is an interface between the panel and equipment that does not speak the fire alarm protocol: lift controllers, HVAC control panels, access control and fire pump controllers.
- Monitored input: supervises one or more normally open volt-free contacts on a single pair of cables and reports changes of state as well as open- or short-circuit wiring faults.
- Relay output: a changeover relay the panel operates according to its programme, opening or closing a circuit in the controlled equipment.
Chapter 21 of NFPA 72 covers emergency control function interfaces: how the fire alarm system operates functions in other systems. The Saudi Fire Protection Code SBC 801 (2024 edition, mandatory since 30 June 2025) covers fire alarm and detection systems in its fire protection systems chapter, and the edition of each referenced standard is the one the code cites or Civil Defense accepts. See AZEIDK’s fire alarm systems solutions.
I/O module or switch monitor?
A switch monitor only watches an input, such as a sprinkler flow switch or valve tamper switch; it controls nothing. An I/O module adds a relay that operates other equipment. If you only need a signal, a switch monitor is enough; see connecting sprinklers to the fire alarm panel. If you need a command, or a signal plus a command, use an I/O module.
Control module vs monitor module in a fire alarm system
Manufacturers give fire alarm interface modules many names, but they come down to two jobs. A monitor module brings a signal in; a control module sends a command out. The I/O module covered in this guide does both in one device.
Monitor module
A monitoring module in a fire alarm system supervises a volt-free contact from a non-addressable device, reports its state to the panel under its own address and supervises its wiring for open and short circuits. AZEIDK examples include the Context Plus SA4700-100IMC switch monitor and the Notifier FMM-1, whose page lists waterflow switches, tamper switches, conventional heat detectors and pull stations on a Class A or Class B circuit. The same family includes the FZM-1 for compatible two-wire 24 V conventional smoke detectors.
Control module and relay module
So what is a control module in a fire alarm system? It carries out a panel command. Some families split it in two: a control module that drives a supervised notification appliance circuit (horns, strobes, speakers) and a fire alarm relay module that provides a dry contact for other equipment. That is how AZEIDK’s page for the Notifier FCM-1 and FRM-1 describes them: FCM-1 for notification circuits, FRM-1 for fans, dampers, lift recall, access control release and HVAC shutdown. On site the same idea is also called a fire alarm interface unit or IFU; these are trade names for the same function.
| Module type | Signal direction | Typical function | Examples AZEIDK lists |
|---|---|---|---|
| Monitor module | Equipment to panel | Flow switch, valve tamper, pump status | Context Plus SA4700-100IMC, Notifier FMM-1 |
| Control module | Panel to supervised notification circuit | Sounders and strobes for a defined zone | Notifier FCM-1 |
| Relay module | Panel to other equipment via dry contact | Lift recall, HVAC shutdown | Notifier FRM-1 |
| Input/output module | Both ways | Command plus confirmation from the equipment | Context Plus SA4700-102IMC, -104IMC, -103IMC; Bosch AVENAR IO module 4000 |
| Zone monitor | Conventional detector circuit to loop | Bringing a conventional zone onto an addressable system | Context Plus 55000-845IMC |
| Loop isolator | No signal; disconnects the shorted section | Protecting the loop from a single short | Context Plus 55000-720, isolating base 45681-284IMC |
Rule of thumb: a signal only needs a monitor module, a command only needs a control or relay module, and a command with confirmation from the equipment needs an I/O module. For Honeywell Gent systems AZEIDK also lists Vigilon interface units, in loop-powered versions and mains-powered versions with their own battery backup.
Fire alarm input/output module types: single, twin or mains switching?
Figures below come from AZEIDK’s product pages and the official Context Plus addressable interfaces datasheet published on the AZEIDK website.
SA4700-102IMC input/output unit with isolator
Supervises one or more normally open contacts on a single pair and provides a set of changeover relay contacts. Loop voltage 17–35 V DC, quiescent current 500 µA, maximum current with LEDs on 3.5 mA. Relay contact rating 1 A at 30 V AC or DC (inductive or resistive), maximum switching current 3 A. The datasheet warns that no supply above 50 V AC rms or 75 V DC may be connected to any terminal. It has a bi-directional short-circuit isolator, IP54 rating and a –40 °C to +70 °C operating range; the product page states LPCB approval.
SA4700-104IMC twin input/output unit with isolator
Two electrically independent I/O circuits in one enclosure, with the same 1 A at 30 V AC/DC relay rating. Suited to two adjacent control points. See the SA4700-104IMC page.
SA4700-103IMC mains switching I/O unit
A volt-free single-pole changeover relay capable of switching 250 V AC at up to 5 A, plus a monitored input. The product page lists nine preset operating modes and a fail-safe mode conforming to BS 7273-4, with applications including door holders, stopping air handling units and fans, and lift recall. See the SA4700-103IMC page.
Bosch AVENAR IO module 4000
For Bosch AVENAR panel projects AZEIDK supplies the Bosch AVENAR IO module 4000, including the FLM-430-I4R2 and FLM-430-I2M1. According to Bosch, inputs and outputs are software-configurable; the FLM-430-I4R2 has four inputs and can connect up to four 4-wire conventional detectors; the FLM-430-I2M1 allows 1,000 m of input and output line length and draws up to 0.72 mA LSN current including alarm current. Relay contact ratings are not on that page, so check the official Bosch datasheet before submittal.
| Model | Inputs and outputs | Relay rating (per source) | Typical use |
|---|---|---|---|
| Context Plus SA4700-102IMC | Monitored input + changeover relay, with isolator | 1 A at 30 V AC/DC | Volt-free control signals to lift, HVAC and access control panels |
| Context Plus SA4700-104IMC | Two independent circuits, each input + relay, with isolator | 1 A at 30 V AC/DC | Two adjacent control points |
| Context Plus SA4700-103IMC | Monitored input + volt-free changeover relay | 250 V AC up to 5 A | Mains loads such as door holders and fans |
| Bosch FLM-430-I4R2 / FLM-430-I2M1 | Software-configurable inputs and outputs | See official Bosch datasheet | LSN loop on Bosch AVENAR panels |
Which module for which equipment?
Lift recall
The panel sends the lift controller a recall command to the main or alternate floor depending on the initiating detector. The lift supplier defines the signal its controller accepts, typically a volt-free contact, so an SA4700-102IMC is usually enough. Use a separate output for each distinct recall function.
HVAC and fan shutdown
If the HVAC control panel accepts a volt-free stop signal, a single unit is enough. Breaking a 230 V supply directly needs an SA4700-103IMC or an interposing relay or contactor defined by the electrical specification. Stair pressurisation and smoke extract fans must keep running during a fire and must not be caught by a blanket “stop all fans” command.
Door locks and door holders
The SA4700-102IMC page lists releasing access control locks; mains-powered door holders are an SA4700-103IMC application. In both cases define how the door behaves on loss of power or loop. Per the datasheet, with failsafe mode set by DIL switch the SA4700-102IMC operates its relay without a panel command on loss of loop or protocol.
Fire pump controller interface
Fire pump controllers usually provide volt-free contacts for states such as pump running and faults, as defined by the controller datasheet and project specification. Wire them to monitored inputs so they appear on the fire alarm panel with clear text, and programme each with the signal type the specification requires: a fault is not a fire alarm. See AZEIDK’s fire pumps.
Where to install, wire and supervise the module
NFPA 72 section 21.2.4 requires the emergency control function interface device to be close to the controlled component. Earlier editions set the distance at 3 ft (0.9 m). In the 2025 edition, 21.2.4.1 keeps 3 ft where conductors are not in metal raceway or metal armoured cable and allows up to 20 ft (6 m) where they are, and 21.2.4.2 exempts Class D control circuits from both limits. The NFPA committee statement makes clear that plastic raceway does not qualify. Confirm the edition adopted for the project before locating modules on drawings. Rule of thumb: the module goes next to the equipment panel, not next to the fire alarm panel.
- Mounting: the SA4700-102IMC and SA4700-104IMC are for indoor use only, surface mounted on the supplied back box or flush in a UK double-gang box at least 30 mm deep.
- Input supervision: the unit returns analogue value 4 on open or short circuit, 16 in normal operation and 17 when failsafe mode is set.
- Cable resistance: 50 Ω maximum per the datasheet.
- Isolators: all three Context Plus units have built-in short-circuit isolators, which affects isolator distribution on the loop. See addressable fire alarm loop design.
Isolator module and smoke detector with isolator base: when do you need them?
An isolator module in a fire alarm system neither monitors nor controls; it protects the loop. When a short circuit occurs, the two isolators nearest the fault disconnect only the section between them and the rest of the loop keeps working; power and data return automatically once the short is cleared. That is what AZEIDK’s page for the Context Plus 55000-720 loop isolator (mounted on base 45681-211) states, with up to 20 detectors, or their equivalent load, between isolators.
A common alternative is a smoke detector with an isolator base, such as the Xpert style isolating base 45681-284IMC, which puts the isolator at a detector position with no extra enclosure. Per the catalogue, up to 20 devices may sit between isolating bases provided their total switch-on surge current does not exceed 20 mA. The Context Plus SA4700-102IMC and SA4700-104IMC I/O units have built-in isolators, so they count in the isolator layout without a separate device.
The number and position of isolators is part of loop design, the project specification and the adopted reference; check them in addressable fire alarm loop design before fixing quantities.
Fire alarm control module wiring diagram and PDF datasheets
Wiring differs from model to model, so never copy it from a previous project or a similar unit. The reference is the installation guide and datasheet of the exact model: loop terminals, input terminals, relay contacts (NO, NC, COM) and any end-of-line resistor the manufacturer requires. Published datasheets and catalogues in PDF are on AZEIDK’s technical documents page, and general loop and zone wiring is covered in our fire alarm wiring diagram guide.
How many I/O modules to order: counting from the cause and effect matrix
Quantities are not a percentage of detector count. They come from the cause and effect matrix:
- Count output columns: each item of equipment or function that must be tested on its own needs its own output.
- Count incoming signals from other systems: pump status and faults, special suppression panel signals, and any state the specification requires on the fire alarm panel.
- Classify each output by load: low-voltage volt-free signal (single or twin unit) or mains load (SA4700-103IMC or interposing relay).
- Group adjacent points: two control points in one room may share a twin unit.
- Add the modules to loop capacity and standby current in the battery calculation, and check in the datasheet how many addresses each unit uses.
Then label each module in the panel programme with the equipment name used on the drawings; see addressable fire alarm panel programming.
How are I/O modules tested at handover?
A relay change on the panel display is not a pass. The equipment itself must respond: the lift reaches the designated floor, the AHU stops, the lock releases. Open- and short-circuit the input wiring to confirm the fault is reported. Where many systems interact, run an integrated systems test; see integrated fire and life safety systems testing.
Common mistakes
- Connecting a 230 V load to a relay rated 1 A at 30 V.
- Mounting the module beside the fire alarm panel and running a long cable to the equipment without checking the NFPA 72 distance rule.
- Using one output for several items that cannot be tested individually.
- Programming a pump fault signal as a fire alarm.
- Ordering modules for a different protocol than the panel, such as LSN modules for a Context Plus panel.
FAQ
What is an input/output module in a fire alarm system?
An addressable loop device combining an input that monitors a volt-free contact from other equipment and a relay output the panel uses to control equipment, such as lift recall or HVAC shutdown.
Can an SA4700-102IMC switch a 230 V fan directly?
No. Its relay is rated 1 A at 30 V AC or DC. Use an SA4700-103IMC (250 V AC up to 5 A) or an interposing relay as specified.
When should I choose the SA4700-104IMC twin unit?
When two control or monitoring points are next to each other. Its two circuits are electrically independent in one enclosure, with the same relay rating as the single unit.
Do Bosch modules work with a Context Plus panel?
No. Bosch AVENAR IO module 4000 units are for LSN loops on Bosch AVENAR panels; Context Plus modules are for Context Plus panel loops. Choose by panel protocol.
How far can the I/O module be from the equipment?
NFPA 72 sets the distance: 3 ft in earlier editions, and in the 2025 edition up to 20 ft with metal raceway or metal armoured cable, with no distance limit for Class D circuits. Check the edition adopted for the project.
What is the difference between a control module and a monitor module?
A monitor module reports the state of a contact from other equipment to the panel. A control module carries out a panel command to a notification circuit or other equipment. An I/O module combines both.
What is an isolator module in a fire alarm system?
A loop device that disconnects the shorted section between the two nearest isolators so the rest of the loop keeps working. The Context Plus 55000-720 page allows up to 20 detectors, or equivalent load, between isolators.
Do SA4700 I/O units need a separate isolator?
The SA4700-102IMC and SA4700-104IMC have built-in short-circuit isolators and count in the isolator layout. Loop design decides whether extra isolators or isolating bases are needed.
Conclusion
The I/O module is where a fire alarm decision becomes action in another system. Count modules from the cause and effect matrix, select each model by load and datasheet relay rating, install it next to the equipment, and test the equipment’s response at handover. That reduces snag items and makes each party’s interface responsibility clear.
Quantifying I/O modules for a project? Send us your cause and effect matrix, panel type and the equipment list to be interfaced, and we will propose suitable Context Plus or Bosch models with datasheets. Contact the AZEIDK team
