I'm also wanting to get a smoke detector system setup through the house. Z-Wave is pretty much out of the question for me at this stage if my understanding of the system is correct (all products on forums are not allowed in NZ due to frequency). I'm in New Zealand and there seems to be only selected few products around from place in Australia (USB hub and appliance controllers).
GC100 looks to be great product but the cost seems very high and as mentioned the Z-Wave $100 detector if needing 4 or 5 is not an option for a lot of people.
Hari how did you get on with the ethernet solution?
Looking for something readily available, affordable solution that won't break the bank!