Also a surprising number of people don't realise that smoke detectors expire. Usually around 10 years. We bought our house in 2015 and when I took one of the detectors off the wall it said it had expired in 2010.
have a look at the hottest deal of the day today, "bankrupt the NHS" the smoke alarm is the same, when they are so cheap buy your own. Tea lights aren't my comment :)
or they just really don't want people to die in the unfortunate event of a fire, next time I'm working at a fire station I'll ask. *edit* don't use tea lights? Why ever not?
this is the link, but probably all gone http://www.morethan.com/home-insurance/news/guide-smoke-alarms-home
Can never be too safe!