According to the UK government, failure to have a working smoke alarm can double your risk of dying in a house fire. Available in many different styles, smoke alarms can be powered by battery or connected to the mains. Both types can go off for reasons other than a fire and for safety’s sake, you should always investigate the matter.
The smoke from a fire could cause a wired smoke alarm to go off. Indeed, this is why smoke alarms exist, to alert people that a fire has started, and give them a chance to evacuate the building. As of March 2013, most smoke alarms on the market are not sophisticated enough to be able to tell the difference between all the different possible causes, so unless you are absolutely sure no fire has started, it makes sense to evacuate the building when you hear a smoke alarm going off.
Steam sometimes sets off a wired smoke alarm, even when there is no fire occurring within a building. This is because steam is a vapour that can enter the grille of a smoke alarm box and be detected by its sensors. If your smoke alarm is sited close to your cooker, for example, and you do a lot of boiling and steaming when you cook, your smoke alarm may go off regularly.
Heat can cause a wired smoke alarm to go off, even when the heat is not caused by a fire. If your smoke alarm is in an area where the air gets hot, for example above a powerful heater or radiator, it may go off when hot air rises and enters the grille of the smoke alarm box. Have your smoke alarm moved to a place where the air is usually cooler to avoid it going off unnecessarily.
If there is no fire occurring within the vicinity of a smoke alarm, nor any steam or heat being produced nearby, a smoke alarm going off could indicate an electrical fault. Since 2005 in the UK, electrical work has had to be carried out in accordance with the strict regulations of The Building Act 1984. This does not mean that you cannot tackle the job yourself but you must do so in a safe and appropriate way.