this one was able to punch through enough walls in our house to work properly. This one uses cordless phone frequencies (2.4Ghz, I think).
In a related note: While baby monitors seem to be too weak to actually function properly, ceiling fan remotes are overly strong! After the second morning of finding the lights on in Ronan's room, we realized that the fan remote in our bedroom was so powerful it was controlling both rooms. I hope there's a choice of frequencies on them that'll work.