Talking of smoke alarms, remember that most of them have an expiry date too. The detector in most smoke alarms has around a 10 year lifespan after which the entire alarm needs replacing.
If I remember correctly, certain groups of people or folks on certain benefits may ask for a free smoke alarm and I think you can even have it installed for you by a handsome fireman too! Certainly worth asking about (and the free alarm is nice too)!