Incidentally, the screwfix mains optical smoke alarm (non-battery
back-up) are a different make to the mains ionisation alarms (battery
back-up) and the instructions state they are not compatible with other
brands!
Neil


Most smoke alarm manufacturers state that their products cannot be
interlinked to another manufacturers alarm.

Also, I prefer to run the smokes (with a battery backup) off the lighting as
it is soon obvious that there is no mains power.

Adam