There's another advantage Zigbee might claim - it uses a published standard, IEEE 802.15.4 for its radio links. But standards aren't documents, says Heydon, they are what is sold in numbers in the market.

And using that radio doesn't even give ZigBee much benefit. "ZigBee doesn't control the radio design," says Heydon. "The only way to really build a low-power low energy system is to build it form the bottom all the way up to the top. The Bluetooth SIG is the only organisation that is capable of doing that."

Other benefits

Heile predicts 600,000 smart electric meters will have ZigBee in them this year, but Heydon thinks Bluetooth has bigger fish to fry: "They can have the electric meters," he says. "You want to control light switches when you are in a chair - and the device you will have with you is your mobile phone."

"The market Zigbee, has been talking about is reducing over time," says Heydon. "The big problem is getting volume and Bluetooth has a big tick box next to it."

It will be a very small additional cost to add low-energy Bluetooth to existing Bluetooth devices, he says, which means the cost of putting it in phones will be close to zero. Silicon companies can start adding it in mid-2009, when the standard is complete, he says, and it should spread rapidly in new mobile phones creating "an instant market" for accessories and home-installed sensors.

This allows other benefits, like presence. For instance, lights can turn on, or your stereo can wake up, when you walk into the room. A car can adapt itself to your preferences when you get in, and a computer can lock itself and maybe turn itself off, when you walk away.

Possibly the most useful thing, though, could be helping find lost items, says Heydon. "If you lose your phone, your watch will tell you where it is."