This is a model 670MBX smoke alarm that includes a 9 V battery back up and can be interlinked to other alarms, If you have the same model as this alarm
It is good until the 17th of December 2029.
I guess it could be used as a battery only alarm but I have no idea how long the batteries would last as the power is normally supplied by the mains and the battery is simply back up in the event of a power cut
Mains smoke alarm with battery back up (Bledlow Ridge HP14)
This offer has been gifted to someone and is no longer available.