An ionisation smoke alarm works by ionising the air between 2 electrodes which are positively and negatively charged, this creates a small current inside the chamber.
When a fire breaks out smoke will enter the ionisation chamber through the opening vents. Smoke alarms from quality manufacturers have the chamber protected with insect screens to stop bugs entering and causing false alarms.
As the smoke enters the chamber, its particles cause the balance of current inside the ionisation chamber to be changed.
Once sufficient smoke enters the chamber the change in current will cause a signal to be sent to the integrated circuit which causes the alarm to sound alerting the occupants to the fire.
Ionisation smoke alarms can be situated on landings, they shouldn't be situated in areas close to kitchens as they are prone to false alarms.
View our other guides to find out how different types of smoke and heat alarms work.
(doc:518 V1.0). Our articles are reviewed regularly. However, any changes made to standards or legislation following the review date will not have been considered. Please note that we provide abridged, easy-to-understand guidance. To make detailed decisions about your fire safety provisions, you might require further advice or need to consult the full standards and legislation.