Optical Smoke Alarm (sometimes known as “Photoelectric”). These types of alarms react best to slow, smouldering fires and should be fitted immediately outside the living area.
In a two storey property industry recommendations are that one of these is fitted either in the living area (if smoking cigarettes takes place) or immediately outside the door of this area on the ground floor.
They are less prone to false alarms caused by steam or cooking.
Mains operated (hard wired) with 9V alkaline battery back up. Battery included.