I don't think anyone knows exactly how it works, except the people at Evolution Robotics (the same people that made/forgot about the ER1 robot). They seem to be very tight-lipped about their technology: they just want you to use it and not wonder about how it works.
That's pretty cool though, and the ability to use additional beacons to cover more rooms creates a fairly simple but powerful intelligent navigation system (I can see people filling their houses with those beacons, having them on every shelf
). It even has limited obstacle avoidance. Personally, I can't wait when people start hacking them (I would like to see someone get Roborealm running on it