Optical smoke detectors
Optical smoke detectors do not contain any radioactive material. Instead it uses a sophisticated photocell system where visible smoke particles is reflected in an infrared light. This system is considerer to be the most effective when it comes to detecting smoldering fires. Fires that can glow for hours before they evolve into fires with an open flame. Examples of this type of fire can be a cigarette lying in furniture, incipient fires in textiles, plastic or if an electrical cable gets overheated. But consider that steam from a shower, dishwasher or boiling water can trigger an optical smoke detector and these places should use a heat alarm instead.
Heat detectors is a compliment for optical smoke detectors and can sometimes be needed where it naturally occurs large amounts of dust particles as in garages, garret, laundry rooms or basements. These detectors is also good for kitchen where sometimes occurs steam which an optical smoke detectors could sound a false alarm. These only react on change in ambient temperature and not of combustion particles. Therefore the use is very limited and it should only be considered as a compliment.
Ionizing smoke detectors
Ionizing smoke detectors measures the electrical resistance in the air and can therefore react on both visible and invisible smoke. Ionizing smoke detectors is considered to be the best when it comes to detect quick starting fires or explosion fires with full combustion, namely fires with an open flame and abundant oxygen supply. This type of fire tends to spread rapidly and produces large amounts of invisible combustion particles. Examples of this type of fire can be fires in a bin, TV or a grease fire in the kitchen. Nowadays ionizing fire detectors are no longer distributed because of the environmental effect the radioactive materials have during the recycling process.