A couple cool hacks here – X10RfConfiguration – essentially converts the fairly unreliable powerline X10 to a more reliable (under many circumstances) RF X10 at virtually no cost and homebrew X10 signal analyzer – rather than measure signal strength, this homebrew signal analyzer (built with a lego mindstorms RCX) actually counts the transmissions that arrive at the destination X10 sensor, for comparison to the source sensor. Missing transmissions indicate reliability problems. Link.