An interesting quote from a spokesperson for ZenSys, (makers of the Z-Wave home automation system).
As interest in these wireless technologies increases for the smart home users, it looks like wireless “congestion” is going to be a major issue. Reliable tracking of people as they move around a house would bring great benefits for any home automation system. Interesting, at this years Defcon meeting, hackers showed a passive RFID tag was able to be read from a distance of over 69 feet. Perhaps more passive devices are a better option for the future.