In the not-too-distant future, your cell phone might become the key to your home. By transmitting a signal to a sensor, your phone will announce your arrival and the front door will unlock.

And that's just the first step. Transmitters in the door will send signals elsewhere in your house, switching on the lights, turning up the heat, warming up the hot tub, queuing up your favorite MP3s on the home theater system, and telling your home computer to power on and download the latest e-mail.

Such fantasies have been a staple of the home automation market for years, of course. They're already being tested in Japan, and they're a bit closer to reality now in the United States, with an emerging home networking standard called ZigBee and some close competitors.

"We're rapidly approaching a world where the most important devices in our lives are ones we don't even realize exist," says forecaster and strategist Paul Saffo, a director of the Institute for the Future, in Palo Alto, CA. Just as cheap microprocessors spawned the PC revolution of the 1980s and inexpensive lasers enabled the telecommunications and Internet revolution of the 1990s, Saffo argues that cheap sensors are ushering in a revolution in intelligent, interconnected devices, many of which will operate quietly in the background, without drawing any attention to themselves.

But before a swarm of sensors can turn into an intelligent network, though, they need a way to communicate with each other. Enter ZigBee. Based on an IEEE radio standard called 812.15.4, it allows digital transmissions of up to 1Mbps in one of two frequency ranges, 2.4GHz or 915MHz (in the Americas).

Overseeing what radio engineers call the upper "layers" of the ZigBee specification, the ZigBee Alliance governs such issues as how packets of electronic information are routed between ZigBee transmitters and receivers, and how these devices interface with various software programs. The alliance also certifies compatible devices and promotes the standard -- in the same way that the Wi-Fi Alliance promotes, certifies, and helps develop the now-universal IEEE 802.11 set of wireless networking standards.

More than 150 member companies already belong to the ZigBee Alliance, including such electronics heavyweights as Honeywell, Motorola, Philips, and Samsung. Alliance chairman Bob Heile claims that ZigBee will enable any compatible device -- regardless of the manufacturer -- to communicate with any other ZigBee device, right out of the box. What's more, the specification allows ZigBee devices to form mesh or cluster networks spontaneously, without any intervention from end users, installers, or (gulp) system administrators.

"When they're being put together by people who don't know beans about networking, these devices have to be intelligent enough that they organize themselves into a network and maintain the network if something breaks," says Heile.