In order to protect your home or business from the risk of fire, you're going to need to install an effective fire alarm system. Now, we all know that a fire alarm alerts you when there is a potential fire or an irregular amount of smoke in your property, but how do they actually work? And what makes a fire alarm different from a regular smoke alarm? IDS Security is here to let you know!

Fire alarms


Smoke alarms

First of all, we need to understand that a fire alarm system isn't complete without a smoke alarm. A smoke alarm is a key part of a fire alarm system - it is the sensor that first detects the possibility of a fire in your home or business through increased levels of smoke. This tiny device, packed with electronics and small amounts of radioactive material, is responsible for reducing the number of fire deaths by half since its widespread adoption in commercial and domestic settings.


How do smoke alarms work?

Smoke alarms fall into one of two categories: ionisation and photoelectric. Ionisation smoke alarms were introduced before photoelectric alarms and are considered effective at detecting flaming fires. Photoelectric smoke alarms, on the other hand, are more effective at detecting fires in their early stages.


Ionisation smoke alarms - As we've mentioned, these smoke alarms are effective at detecting advanced fires and work similarly to how a window-sensor intruder alarm works. Here, there is an electrical circuit present and when this circuit is broken, the alarm sounds. The only difference between an ionisation smoke alarm and an intruder alarm is that there is no physical contact between the two sensors. They work in the following way:

  1. Wires extend from both the positive and negative ends of a battery in the detector.

  2. These wires attach to separate electrodes.

  3. The electrodes complete a circuit but not in a physical sense. Instead, Americium-241 (a radioactive material) transforms the air molecules between the electrodes into positive and negative ions.

  4. These charged ions between the two plates complete the circuit.

  5. In the process of a fire, smoke enters the smoke alarm through holes or slits in the housing unit.

  6. Both positive and negative ions seek the smoke, not the plates.

  7. The circuit is then broken and the alarm sounds.


Photoelectric smoke alarms - Also known as optical smoke alarms, photoelectric smoke alarms alert you when an LED light within the alarm chamber is broken. These alarms are capable of detecting a fire in the early stages before it breaks out into a fully-fledged fire. These smoke alarms work in the following way:

  1. An LED casts light in a straight line across the inner chamber.
  2. A photoelectric sensor at the opposite end detects the light, notifying the system that the circuit is complete.
  3. Smoke enters the alarm housing and interrupts the light, redirecting it to a different sensor.
  4. When this other sensor detects the light, an alarm is sounded.


Fire alarms and how they work

Fire alarms are slightly different to smoke alarms. A smoke alarm simply detects when there are unusual levels of smoke present in the immediate area; fire alarms, on the other hand, detect the high levels of smoke and then act on it.

The sensors are connected to an alarm system that sounds when the detection system is activated. Some fire alarm systems come with an attached sprinkler system that sprays down water from your ceiling in an attempt to put out the fire. However, if your fire alarm system does not include this, it should alert both you and your nearest fire brigade to put the fire out.


The differences between smoke and fire alarms

The main differences between smoke and fire alarms are:

  • A smoke alarm simply acts as a sensor and detects the smoke, while a fire alarm acts on it.

  • A fire alarm system consists of several different devices - including a smoke alarm - all of which are connected together to give your home or business protection against fire. It can alert and even take countermeasures against the fire if it has been integrated with the correct appliances.

  • As we mentioned at the beginning of this blog post, a smoke detector is usually integrated into a fire alarm system. It forms a part of it and is required in order to perform its functions effectively.


Our fire alarm systems

Here at IDS Security, we specialise in the design, installation and maintenance of fire alarm systems for commercial, public and residential properties. We cover all categories of fire detection system, from conventional formats through to large, networked, multi-panel addressable systems.

If you would like to request a quotation for your own fire alarm system, please call 02920 753 251 to speak with a fire protection specialist at our office in Cardiff, or email us at

Learn More About Our Fire Alarms >

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