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How Does a Fire Alarm System Work?

This article is a collaborative effort, crafted and edited by a team of dedicated professionals.

Contributors: Muhammad Baballe Ahmad, Mehmet Cavas, Sudhir Chitnis, and Zhen-ya Liu.

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A fire alarm system is a vital part of any commercial or public building. It is designed to detect and warn people of a fire in the event that one should break out. But how does a fire alarm system work?


Fire alarm systems are designed to detect and alert building occupants of a fire emergency. They are typically comprised of various components, such as smoke and heat detectors, manual pull stations, fire sprinkler systems, and audible alarms. Understanding how these components interact with each other is essential to having a properly functioning fire alarm system. In this article, we will provide an overview of how a fire alarm system works.

What is a Fire Alarm System?

A fire alarm system is a group of electrical devices that are interconnected for the purpose of detecting smoke, heat and other environmental changes associated with fire. The system typically features a network of smoke detectors, manual call points and an automatic control panel. When any one of these components senses an hazard, it will trigger an audible alert to alert building occupants and sound their evacuation in the event of a fire.

Generally, the fire alarm system consists of several different parts: the control unit, visible devices like heat detectors or pull alarms, initiating devices such as manual or automatic fire detection systems, notification appliances like bells or horns or strobes and power supplies that run on either AC electric power (including battery backup) or low-voltage DC power. The components are connected using special wiring to allow communication between all aspects of the system.

When any single device detects an increase in temperature or exposure to smoke particles, it sends a signal through the wiring to activate all other elements connected to its network – allowing for quick responses and maximum safety during emergency situations. Additionally, some building may also be equipped with two-way communication systems that can help building owners talk with occupants during an emergency situation.

Components of a Fire Alarm System

A fire alarm system is a network of interconnected components used to detect the presence of a fire. A typical commercial fire alarm system comprises several separate elements working together to provide protection from the devastating effects of a fire. The components work together in unison to make certain that a quick response is possible in detecting and preventing damage from fires.

The main components of a fire alarm system are sensors, control panels, manual pull stations, bells or horns, and notification appliances such as sounders and visual alarms. Additionally, there may be smoke dampers and other auxiliary devices that complete the system.

Sensors: Fire sensors detect smoke particles or changes in heat in an environment before any flames visibly appear. There are several types of smoke-detection sensors: Ionization sensing technology; Photoelectric sensing technology; Aspirating Smoke Detection (ASD) technology; Combination ionization/photoelectric Smoke Alarm Sensing Technology; Heat detectors also sense temperature increases which can alert personnel before external flames become visible – they come in fixed temperature or rate-of-rise models.

Control Panels: One or multiple control panels form the center point for all systems elements – Sensor wiring terminates at one location for ease of maintenance and access for emergency personnel; one control panel can accommodate thousands of sensors but size will depend on design objectives determined when doing an assessment installed by an expert technician. Manual Stations: Manual pull stations manually trigger alarm events and are typically located near emergency exits. This allows staff or inhabitants in the protected building to call for help if necessary without increasing risks by having to move closer to potential flame sources. Bells/Horns: Signal devices (Bells and Hornets) act as audible warning during an emergency to notify personnel on site and trigger evacuation procedures Notification Appliances: This often colored strobe lights produce audible tones that notifies people even with their hearing aids removed while sleeping or while they engaged in activities like loud music that restricts their ability to hear standard tones produced by signal devices Smoke Dampers/Auxiliary Devices: These allow you control the spread of smoke within ventilation systems during an emergency event which greatly reduces potential property damage losses due to swift attenuating – it’s important that these dialogues are tested regularly according to state codes


Fire alarm systems are designed to quickly detect and alert people of an emergency situation in a building. Fire alarm systems employ detection devices such as smoke and heat sensors, which are connected to a control system. If an alarm is triggered, the control system will activate a loud siren or bell to alert people in the building of the emergency. In this section, we will look at how a fire alarm system detects a fire.

Smoke Detectors

Smoke detectors comprise a major component of any fire alarm system. Smoke detectors are placed in every room of the house where a fire could be likely, such as around windows, on the ceiling in each bedroom, and near the baseboards throughout the home. The smoke detector will typically have two parts: a tab that opens when smoke enters and a microswitch that’s responsible for setting off the alarm.

When smoke enters through the opening, it passes over an infrared-emitting diode (LED) and is reflected back to an infrared-sensing transistor. If enough smoke particles pass between them to raise their heat levels to what’s predetermined as dangerous, then they’ll trigger an alarm, typically sending out both a loud noise indicating danger as well as signalling other interconnected systems or monitoring services such as fire departments. Some models even send off visual cues like flashing lights that let homeowners know of potential issues.

Heat Detectors

Heat detectors are one of the main types of detection systems that are used in a fire alarm system. Heat detectors are designed to sense the heat generated by a fire and set off an alarm. They come in two main types: fixed temperature and rate-of-rise devices.

Fixed temperature heat detectors are calibrated to trigger an alarm at a specific temperature – usually between 135F (57C) and 165F (74C). Each type of detector should be installed in the appropriate area based on its individual specs. While they can respond more quickly than other detectors, they may not be able to detect small or smoldering fires, which produces only low levels of heat.

Rate-of-rise (ROR) heat detectors monitor changes in the temperature around them, such as sudden increases from a fire’s rapid heat production rates or intensifying temperatures due to inefficient ventilation or insulation near sources ignited by the fire. These devices will not set off an alarm until their internal thermometers detect temperatures outside their normal range; this range is typically between 8 – 12 degrees Fahrenheit per minute (4 – 6 degrees Celsius per minute). In emergency situations involving intense fires, ROR detectors will trigger alarms much faster than fixed temperature models as it is more sensitive to intense but short-term heating events.

Carbon Monoxide Detectors

Carbon Monoxide (CO) alarms are an important part of any home safety system and should be placed in each sleeping area. High levels of CO are odorless, colorless, and tasteless, making them very difficult to detect without an alarm system.

A CO detector is basically a specially designed sensor that reacts to changes in the air’s carbon monoxide concentration. The sensor measures the level of CO in the air and then triggers an alarm if it exceeds a certain threshold, usually around 30 parts per million (ppm). The most effective detectors use both electronic sensing mechanisms as well as physical plugs that contain chemicals which react with monoxide gas, indicating there may be higher concentrations present.

When choosing a CO detector for your home, it is important to choose one with digital readouts so you can check what level of carbon monoxide is present at any given time. It is also worth noting that digital detectors are more accurate than those with plated sensors or plugs because they can detect any fluctuations in the levels on a continuous basis. Additionally, many modern detectors will come equipped with technological features such as battery back-up functions and automated alerts that can warn you when levels go above recommended thresholds. By taking all these precautionary measures you will have peace of mind knowing that your home is safe from dangerous levels of carbon monoxide gas.


Fire alarm systems are designed to detect an emergency situation, such as an Addressable Fire, and notify people of the danger. These systems are typically composed of sensors, an alarm, and an indicator that is triggered when a fire alarm is set off. The alarm and indicator will alert people of a potential danger in the area, so that they can take appropriate action. Let us take a look at how an Addressable Fire alarm system works to ensure that everyone is notified of the danger.

Bells and Horns

Bells and horns are connected directly to the fire alarm panel and are generally installed in locations that can be easily heard throughout the building. Once a fire alarm system is activated, the bells and horns will initiate an auditory signal to alert people in all areas of a building, even those where there is no power source. As with other components of a fire alarm system, bells and horns will typically be wired directly into an AC power source as well as a battery backup, so they continue working during power failures.

The loudness of the bell or horn signals can be varied, depending on the class of equipment used in any particular installation. In all cases, bells should have a loudness ranging from 75 dBA to 95+ dBA – measured at 10 feet from the notification appliance – so that occupants are not only alerted when they are close to the notification device itself.

Visual Signaling Devices

Visual signaling devices are an important safety feature of modern fire alarm systems. These devices will alert people in the building by making them aware of any possible danger. Common visual signaling devices include bells, videowalls, voice evacuation systems, and strobe lights. Bells are the most basic and lowest cost option for alerting occupants of a potential fire. Bells will produce both an audible and a visible signal when activated. Videowalls are very loud and will display visual messaging when activated to direct occupants to safety. Voice evacuation systems use pre-recorded messages over loudspeakers that provide instructions during a fire emergency. Strobes are inconspicuous yet powerful flashes of light that draw attention quickly when in danger arises. All these signaling devices should be tested regularly to ensure that they operate correctly if a real emergency were to arise.

Voice Evacuation Systems

Voice Evacuation Systems are designed to alert occupants of danger within a building. This type of system is used in conjunction with a fire alarm system, and typically includes speakers that produce notifications such as pre-recorded verbal audible messages. Voice Evacuation Systems are typically located inside the buildings and strategically placed throughout the facility. By using a combination of tones, words, and instructions, the system will direct occupants to make orderly exits swiftly and safely.

The most effective way to activate an evacuation is through verbal commands spoken over an emergency loudspeaker system. Emergency voice communication systems will work with existing fire alarm systems to quickly alert occupants and help guide people to safety in emergency situations. To achieve optimal results, voice evacuation should be loud enough for all occupants in the area to hear clearly yet be adjustable enough so that it doesn’t overwhelm them or cause confusion. With no time to waste during emergencies, having intelligible sound levels for alarms is crucial for successful occupant rushing scenarios. It is also important for administrators or building managers to have access control options such as restricting access based on identity credentials or allowing one-time broadcasts that would provide immediate guidance in case of emergency evacuations involving large numbers of people.

Control and Monitoring

Fire alarms systems provide a critical layer of safety that detects smoke and heat, alerting people of a potential fire. The system is made up of a set of interconnected components that work together to detect, control and monitor any potential fires. Let’s take a deeper dive into how fire alarm systems work, looking at the elements that make up the system and how they interact with each other to detect and respond to a fire in your building or home.

Manual Control

Manual control is typically carried out through the use of a panel, placed in a convenient location, known as the fire alarm control panel (FACP). The FACP consists of two major components: an indicator panel and manual release controls. The indicator panel displays information about the operation of the system, including alarm or fault conditions, power status and internal or external device failure messages. Manual release control buttons allow for manual activation of specific devices in an emergency, such as pull stations or sprinkler systems. In areas where detection systems are not installed, these buttons can be used to manually initiate alarms.

Automatic Control

One of the essential components of any fire alarm system is the automatic control. This device acts as a nerve center for the entire system, providing a continual communication link between all the parts. It monitors and controls electrical conditions in the wiring circuits and ensures that each monitoring device transmits and receives information from the main panel. The control also sends messages to other components, such as bells and sirens, letting them know when to turn on or off. As an added measure of protection, some systems use emergency power supplies that kick on in the event of a primary power outage.

Remote Monitoring

Remote monitoring is an alarm system that allows for offsite monitoring activity by central station personnel. This type of monitoring provides notification of events that require dispatch of fire or police personnel, as well as other building safety services. With this system, a fire alarm call can be made to the central station and location dispatchers can be alerted quickly, regardless if a building employee initiates an inspection.

The connection between the fire alarm panel located on the premises and the service provider’s monitoring center will usually use a dedicated communication link such as cellular or radio frequencies that provide uninterrupted signals that are encrypted and cannot be intercepted easily. This link will also allow two-way communication where a central station operator can obtain additional information from someone onsite if need be during an emergency. The remote monitoring system also can provide real-time data for ongoing facility management tasks such as system testing, scheduling maintenance activities, and even deactivating false alarms in progress so local authorities are not dispatched.


Fire alarm systems require regular maintenance in order to stay in proper working condition. For instance, fire alarm systems need to be tested periodically for proper functionality, and their batteries should be replaced regularly. Additionally, the system should be inspected for any signs of corrosion or wear and tear, which can indicate that parts need to be replaced. It is also important to clean and inspect the system’s sensors and detectors to keep them in optimal condition.

Test and Inspection

Test and inspection of fire alarm systems is an important component to ensure that the system will function as expected in the event of an actual fire. Depending upon the type and size of system, different codes and standards can apply. Generally, routine tests should be performed in order to determine if any components have failed or fallen into disrepair. These tests should include visual inspections, functional testing, calibration of all devices and components, repair or replacement as necessary for all devices and components, battery testing, operation tests for both audible/visible notifications as well as other systems integrated with the fire alarm system (if applicable). Additionally, some areas may require a certified fire alarm technician to conduct required tests – check with your local authorities before performing any maintenance tasks.

Cleaning and Maintenance

Regular cleaning and maintenance of a fire alarm system is necessary for both proper functionality, and for insurance and legal requirements. This can include, but is not limited to, cleaning detectors, testing all components of the system, performing system calibrations, ensuring all parts are in good working order and up to date with regard to code compliance.

Detector cleaning is important both for accuracy and for maintenance of the equipment. It ensures that dust does not build up on detector lenses or surfaces that may otherwise cause alarms to sound unnecessarily. Cleaning should be done with regularity depending on the environment in which the detectors reside-dusty settings may require more frequent cleanings than those that are relatively clean. Generally speaking, cleaners should use compressed air in a can or small vacuum cleaner (avoiding contact with electric wires).

System tests should be done on a regular basis as well: weekly or monthly depending on the site’s needs and particular conditions. Tests should involve manually setting off each device to test its range as well as assessing appropriate response time. Once tested, all components should be checked again before resetting them according to manufacturer’s guidelines. Depending on their sensitivity thresholds, some detectors may need occasional calibration or adjustment so they respond properly when triggered.

Overall care should be taken to ensure all components are regularly inspected/serviced by qualified personnel; codes updated/upgraded if necessary; batteries replaced/maintained according to requirements outlined by manufacturers; documentation kept up-to-date; records retained of work completed; reports filed when requested by authorities; wiring checked regularly for any faults etc., in order for a fire alarm system to work efficiently so it can provide optimum protection for those using its premises from potential dangers posed by fire hazards.

Battery Replacement

A regular maintenance schedule must be adhered to in order to keep a fire alarm system in proper and optimal working condition. One important component of this regular maintenance is battery replacement. In general, 9-volt, 12-volt and 24-volt batteries are used in fire alarm systems and have a recommended lifespan of three to five years depending on the type of system and battery.

It is important for personnel responsible for the maintenance and upkeep of fire alarm systems to inspect the batteries regularly and replace them when necessary. Faulty or damaged batteries can result in a false alarm at best or a delayed response at worst. A full assessment should be done twice a year – during spring cleaning for smoke alarms – and during fall cleaning for carbon monoxide detectors – although inspections should happen more frequently if there is any heightened risk or concern with the particular system.

Before conducting any routine checks or replacements, it is important to make sure that the power supply has been shut off prevent shock hazards, as well as disruption with other connected devices or systems if necessary. It may also be necessary to consult manuals specific to each model when replacing batteries so that correct installation procedures are followed correctly.

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