We already decided to install a sprinkler system because of the distance to the fire dept and lack of hydrants. If you are using PEX for plumbing I recently saw a PEX based sprinkler system that uses the existing PEX runs. You would think it would be cheaper to install but it isn't the PEX is cheap but the heads cost $25 vs $3 each so the total costs runs about the same as a regular sprinkler system.
I've heard of another residential type system that generates a fine mist to control (notice I said control not extinguish) the fire. IIRC it uses about 10 gals. Supposedly you would have time grab your CO2 extinguisher or get everybody out of the house before the fire got out of control.