Ionization vs Optical Smoke Alarm: How to Choose

This article could be useful to you if:

  • You have just moved into a new home with no fire alarm system installed.
  • Your existing fire alarm system no longer works.
  • You previously neglected to install a fire alarm system to your home.
  • You wish to extend your fire alarm system to cover more of your property (for example if you have just built an extension or an outbuilding).

Types of Smoke Alarm


Ionization Chamber detectors

The fancy name might suggest otherwise, but this is the simplest and most common type of smoke alarm. They actually contain two small samples of americium-241, which is a radioactive isotope. This radioactive material emits a steady stream of radiation which is disrupted by smoke particles that enter the device.

One piece of the material is in a sealed chamber, the other is exposed to the air where smoke will flow through. The device compares the currents generated by the radiation of each sample and when they differ by a sufficient amount, the alarm goes off.

So, that innocent looking smoke alarm you thought was keeping you safe is actually busy firing radioactive beams; very small amounts and within the alarm casing however, so there’s no risk unless you start taking it apart. Despite the radioactivity, small numbers of smoke alarms can be safely thrown away with the rubbish.

Optical Detectors

An optical detector just uses a light source and a detector which picks up if dust particles are scattering the light beam.  Whilst these types of fire alarm do provide warning for all types of fire, the problem is that they take longer to register the presence of the smoke than the ionization chamber types. A fast igniting flame will be picked up far faster in the ionization type. This is due to the size of the particles within the cloud. A cloud emitted from a slower, smoldering fire has larger particles than a faster igniting flame.

The advantage of using an optical detector however, is that it won’t go off from kitchen fumes and the like that can cause false alarms with the more sensitive ionization chamber type of smoke alarm.

Choosing which smoke alarm to install

You should install optical alarms where harmless fumes will be emitted, such as kitchens or where air circulates with kitchens.

Ionization chamber alarms should be chosen elsewhere due to their increased sensitivity to dangerous fast growing fires. If you’re still worried about the radiation, read this to set your mind at ease.

In our next article we will cover how best to position your smoke alarms.

2 Responses to “Ionization vs Optical Smoke Alarm: How to Choose”
  1. I paid $2400.00 for 4 smoke alarms and 2 heat alarms for attic and Kitchen areas model RF-360T combination alarms with interlinx optical . also does the optical provide more protection than the ionization smoke alarms or did I get ripped off I am a senior on a fixed income went to a seminar and fell for a scare-tactic. I am afraid . please respond

    • Hi Elizabeth, sorry for the late reply. Optical does provide more protection in one sense. This is because as time passes, smoke clouds become more disparate and optical alarms are good at detecting low concentrations of smoke. Thus for locations with low risk of fire, optical is a good choice as any smoke that arrives at these locations will have thinned out. These more distant locations will also be lower risk so the delayed problem optical alarms have will be less of an issue. However if there is a fire in the vicinity of the alarm, then they will be relatively slow in detecting this.

      Heat alarms are a good alternative to smoke alarms for a kitchen where fires are more likely. Smoke and vapour generated from normal cooking activity will not set off false alarms with these.

      However, $2400 seems like far, far more than you should pay for alarms of these types. I would typically pay around $60 dollars in total for 4 fully functioning and reliable smoke alarms and 2 heat alarms.

      If you can try and return those alarms you bought that would be ideal and shopping on in future will really help you out to get good value products.

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