People are quite good at having a smoke-alarm but very bad at making sure it works as it should. Most people know that it needs to be done, yet somehow it doesn’t get done. Forgetfulness is the biggest reason, but also ignorance can play a part, maybe you do not know how to do it. Many people rely on hearing the “beep” when the battery is running out, but you can miss this if you’re away for an extended time, for example on holiday.
A survey in Sweden showed that a quarter never tested their smoke-alarms. Forgetting, laziness and ignorance were the most common reasons. Nine percent had out of date, old smoke-alarms and four percent didn’t even have one.