"Andrew Gabriel" wrote
| fire alarms = either wire from a regularly used lighting circuit,
| or give own small radial circuit (i.e. B6A or B3A MCB).
| There are some rules (which I don't remember, and didn't seem very
| sensible to me) about sharing smoke detectors with lighting circuits,
| and relate to the type of battery backup the smoke detectors have.
| In my case, the smoke detectors run off the alarm anyway, and use
| the alarm battery in the event of a mains failure.

IIRC if you use a lighting circuit (where you will probably notice a failure
fairly quickly) you have to have battery[1]-back-up smoke detectors, and if
you use a dedicated circuit (which would go faulty for weeks without being
noticed) you don't have to have battery-back-up.

Owain

[1] Although some have a whopping big capacitor these days, I think