Types O f Fire Detectors

Did you know that there are actually four different types of detectors that are used to sense the presence of a fire? Curiosity takes people to find important information. Today, your curiosity has brought you to this guide on the types of fire detectors. Fire can be deadly when it’s uncontrolled. After you must have read through this guide, you should know the types of fire detectors, and also their various purposes.

Fire detectors are devices with sensors built into them that are capable of detecting one or more of the products or phenomena resulting from a fire. They are a key component of a fire protection system, which consists of several subsystems including at minimum the fire detection devices, the notification and/or suppression activation, and a controller that receives the signals from the detection devices to initiate the appropriate actions.

While all of these components are equally important for the system to function properly, it’s easy to see how dependent the system is on having the right initiating devices for the detection system – the wrong detection devices or improperly functioning detectors can cost lives.

Types of Fire Detectors

There are four main types of fire detectors that can help you protect your building. Once you know the difference between the detectors, you’ll be able to decide which one is right for your building.

The main difference between the four fire detectors is whether they detect heat or smoke. Overall, the best choice would be to buy an ionization and photoelectric detector. However, that could vary depending on what type of building you have.

Main Types of Fire Detectors

Heat Detector

Heat detectors are generally used in storage closets, warehouses, or other rooms that aren’t frequently occupied. They will alert you when there’s a rise in the room temperature or if there’s a significant amount of heat in the room. The issue with heat detectors is they take a little longer to detect a fire than smoke detectors. However, they have fewer false alarms because they don’t go off when there’s steam, dust, humidity, or precipitation.

False alarms may be triggered in buildings that are abnormally steamy, dusty, or humid and are best suited for buildings that are not continuously occupied such as warehouses or storage facilities.

Heat detectors can be wired or wireless. Most home security experts recommend that homeowners use wireless, battery-operated heat detectors. Using batteries will make sure that the heat detector continues to work even if the power in the house is shut off.

Wired alarms may face challenges during neighborhood blackouts. The batteries that are used to power heat sensors are extremely reliable and have been known to last up to 10 years without failing. However, to be safe, heat detectors batteries should be replaced every five years.

Heat detectors are basically of two kinds: Rate-of-rise (ROR) heat detectors and fixed temperature heat detectors.  Heat detectors are used in areas where smoke alarms are not suitable. Heat detectors are quite hardy and can withstand very harsh environmental conditions. They are very useful in areas where there are high levels of fumes and dust.

Heat detectors must not be installed in areas that have very high humidity levels as the humidity may prevent the heat from entering the heat detector unit and may cause the alarm to fail and not get activated. Also, installing heat detectors in areas where temperatures may rise above 100°F, fall below -10 °F, or near fluorescent lights, may affect its operations.

  • Rate-of-rise or (ROR) Heat Detectors

ROR heat detectors work on the rapid increase in the element temperature of around 12°F – 15°F per minute. This rise in temperature does not depend on the initial temperature. ROR heat detectors work on the principle of thermistors or thermocouples.

The ROR detector has two thermocouples that are sensitive to heat. One of the thermocouples monitors heat that is transferred by radiation or convection. The other thermistor responds to the ambient temperature. The heat detector is activated when the temperature of the first thermocouple increases relative to the second one.

ROR heat detectors may not respond too slowly developing fires. In order to detect slowly developing fires, usually, a fixed temperature element is added to the ROR detector which will be activated when the element reaches the pre-set threshold temperature.

  • Fixed Temperature Heat Detectors

These types of heat detectors are the most commonly used. Fixed temperature heat detectors work when the element that is sensitive to heat reaches the point where a solid changes to a liquid. The heat is accumulated at the sensitive element due to a thermal lag.

This causes the temperature of the device to reach its operating temperature a while after the surrounding air temperature exceeds the device temperature. When this happens, the detector is activated and an alarm is sounded.

Ionization Smoke Detector

Ionization smoke detectors are usually found in commercial kitchens and restaurants. They activate when there’s smoke present in the air. The detector has two metal plates inside, which have a constant electric current that flows back and forth. Once smoke enters the chamber, the current will no longer flow and the alarm will sound.

Photoelectric Smoke Detector

Photoelectric detectors are great for detecting small fires. They are similar to ionization detectors, but instead of using an electric current, they use a beam of light to detect smoke. When smoke enters the chamber on the photoelectric detector, then it will interfere with the light and the alarm will go off.

Ionization and Photoelectric Smoke Detector

A smoke detector that senses both ionization and photoelectric smoke is the best way to arm your building. This detector combines both the ionization and photoelectric detectors to work as one unit. When there’s smoke in the air, it will disrupt both the beam of light and electric current, which will cause the alarm to sound. The best thing about this detector is it works as a 2-in-1 system, however, it won’t be able to detect heat.

Factors to Consider When Choosing Fire Detectors for Your Business

As you can probably see, no single method of fire detection is universally applicable. They all have their strengths and weaknesses. And, given the wide variety in the types of fires that can occur and the many different applications and environments in which they are needed, every application is going to be unique.

Understanding your fire risk is essential to choosing the right devices. The list below provides several factors you should consider before making any selection.


  • Nature and quantities of combustible materials present:
  • Their ease of ignition
  • Likely form of combustion
  • Their propensity for smoke production
  • Heat release rate
  • Probable rate of fire growth and spread


  • Temperature and humidity
  • Cleanliness
  • The extent of any pollutants present
  • The type(s) of work processes that occur in the area
  • The proposed fire evacuation strategy;
  • Other active and passive fire protection measures present.
  • The susceptibility of contents to heat, smoke, and water
  • The height and geometry of the protected area
  • Other active and passive fire protection measures present

Once you have a clear understanding of your fire risk, you will be better able to identify at least generally, which types of detection devices you need – smoke detectors, flame detectors, fire gas detectors, or some combination of these.

For any device you are considering, always evaluate the performance criteria to ensure it will meet your unique needs, including the speed at which the device can detect a fire and any interferences or other vulnerabilities that can lead to unintentional alarms.

Smoke and Heat Detectors

BS 5839-6:2019 recommends that smoke and heat alarms be installed:

  • On the ceiling, as central as possible in the room
  • Sited 300mm from walls and light fittings – this ensures the alarm is out of any ‘dead air’ spaces where the airflow may be blocked
  • Placed within 3m of every escape door and bedroom door to ensure audibility
  • Positioned between high-risk rooms and bedrooms
  • For peaked and sloped ceilings – make sure there is a maximum of 600mm vertically down from the apex for smoke alarms, and 150mm vertically down for heat alarms.

The strengths of smoke detectors are:

  • Detects Fires Quickly. Smoke detectors are the fastest way to detect fires. Since smoke is produced as soon as the fire starts, the detector can alert the homeowner seconds after the fire starts.
  • Smart Capacity. Smoke detectors can be “smart,” meaning that they can be installed with a wireless home security system and synced with your mobile device. With this ability, the smoke detector can alert the homeowner to a house fire even when the homeowner is away. Rather than waiting for a neighbor to notice flames in the window, smoke detectors allow homeowners to proactively protect their homes and call for the fire department seconds after the fire has started.
  • Detects Low Energy Fires. Not all fires are the same. Some fires, called low energy fires, emit only a small amount of heat but lots of smoke. These fires are hard for other fire detectors to sense. A smoke detector, on the other hand, can detect low energy fires faster than any other device on the market.

The strengths of a heat detector are:

  • Less Prone to False Alarms. While smoke detectors are prone to false alarms, heat detectors are harder to fool. Heat detectors rely on the actual temperature of the room, and, if the temperature of the room hasn’t increased, the alarm won’t be activated.
  • Protects Attics and Basements. Smoke detectors struggle to protect attics and basements due to the dust and other particles in the air. Heat sensors, on the other hand, can easily protect their areas without losing their efficiency. They maintain their effectiveness in a variety of rooms and situations.
  • Used With Ceiling Sprinklers. Heat detectors are the number one choice for triggering ceiling sprinklers in a building. The last thing that a business would want is a false alarm that activates the sprinklers. However, if there is a fire, ceiling sprinklers can save the building. Because heat detectors are incredibly effective and hard to fool, they are the best choice for this job.


A combination smoke detector is the best way to protect your facility and its occupants from a fire. When both forms of smoke detection are together on one device it helps to ensure that regardless of the type of fire, it will be detected as soon as possible.

However, an addition to a heat detector is important for your protection. Also, they are often used to trigger fire sprinkler systems or fire suppression systems. If a smoke detector was hooked up to a sprinkler system it could trigger the water during a false alarm, and water damages your building.