Smoke/heat detector regs

Effects

I'm going to put a smoke/heat detector circuit in a holiday home I have that hasn't had one previously. I'm a bit rusty on regs so just wanted to check. It's a three bed bungalow. I was going to put a heat in the kitchen, a smoke in the joining living room, a smoke in the hall outside the bedrooms and another heat in the sitting room at the end of the hallway. Is that enough to cover it? Also, can I wire it in three core .75 flex using the earth as the link?
Is there anything I'm missing?

meercat

Depending on layout of your bungalow
Heat kitchen
Smoke main living room
Smoke enterance hall
Smoke other end hall(outside bedrooms)

If in doubt you can always add another to be sure

Wire in 1.5 t&e with 1.5 PVC/PVC interlink

Effects

Thanks for the reply. Is there a reason I shouldn't use flex? I thought having it in a single cable might be neater. That said, I do have about 4 coils of 1.5 pvc/pvc lying around.

tomdempsey200

flex is allowed for fixed wiring
1.5 minimum
gr/yellow for interconnect not allowed
it's 4-5 alarms for building regs
if you go onto the EI website they've got some good guides