Test all your smoke alarms every month to make sure they are working.
All smoke alarms hard-wired or battery operated, are manufactured to a standard that requires them to have an effective life of 10 years. After this time, their efficiency can be compromised or they may malfunction.
The use by date, or date of manufacture, should be stamped on the alarm, so check this yearly when you change your batteries.
If any of your alarms are 10 years old replace them straight away.