Wireless sensor networks is a Hot Technology. At this week's Wireless Sensing Solutions conference in Rosemont, Illinois, one group of people talked endlessly about the incredible things you'll be able to do in the future, while another just asked questions, trying to figure out how they can actually make money with the networks.

Wireless sensors use an array of radio technologies, many of them proprietary, some of them familiar such as Bluetooth or even one of the flavours of 802.11. Growing in use is a very low-power, short-range radio based on the IEEE 802.15.4 (Zigbee) standard.

The ZigBee Alliance, an industry consortium with about 100 members, adopted that standard, and then added networking software and an application framework. Several vendors are now offering ZigBee radio chipsets and protocol stacks.

These wireless nets typically are meshes: a radio-equipped sensor can discover its neighbours, while routing software sets up multiple connections, so traffic can always find a path, and can route around failures or gaps. Each node can also act as a router or a repeater, or these functions are assigned to specific coordinating nodes.

What would you do with a wireless sensor?
But this week the focus is less on the excitement than on practicality. "You don't ask people, 'how would you use ZigBee?' Because they don't know," says Ken Douglas, recently named to be BP International's first director of technology and sensory networks, in the oil company's chief technology office. "But if you ask them, 'how would you use information that you can now access for the first time?' They have to think about it for a bit, but then the ideas just starting pouring out."

Gerry Nadler, chief scientist for MachineTalker in California, said he'd met at the conference a woman with a US Air Force logistics unit. She told him, he said, that her group had 200 forklifts that were suddenly ordered to Kuwait. They were loaded onto cargo jets and flown to the Middle East. But when they arrived, the batteries were dead, and there were no recharging units available: the urgently needed gear was useless. "I told her that with our products you could create a sensor network that would wirelessly monitor the battery charges so that would never happen," Nadler said. Her reaction, he said was: 'Gee, you can do that?'

Harris Kagan, an executive with Invensys, a British automation and controls systems integrator, said he recently asked a Nabisco executive what was the most important thing he wanted to know. The reply came without a moment's delay: "I'd like to know the moisture content at the centre of the cookie when it reaches the middle of the oven."

Cement and sugar beets
The need for that kind of precise knowledge was the driver for a kickoff session Tuesday morning, titled "30 applications in 60 minutes." Ten speakers outlined applications that captured temperature or pressure or vibration or other data via sensors meshed together over low-power, short-range radio links. Most of the actual applications turned out to be pilots or demonstrations, usually involving at most a few score of sensors. And many of these are in areas associated with traditional wired sensors, such as industrial automation and building controls.

But the most intriguing applications, the ones that showed the explosive potential for wireless sensing, were the ones that came out of the blue, utterly unexpected. One involved cement, another sugar beets.

Rick Kriss, chief executive of Xsilogy in San Diego, described an application that involves embedding a Xsilogy sensor, coupled with a Bluetooth radio, into cement as it is poured to form a concrete piling. When the cured piling is slammed into the ground by massive hydraulic hammers, the sensor readings pick up characteristics of the waveform created by the impact and reflected by the surrounding soil. The data is transmitted to a nearby gateway and analysed.

The reading shows the kind of soil on which the piling is grounded and the piling's load carrying capacity. That information can reduce the number of pilings and the amount of concrete in big construction projects, saving millions of dollars, Kriss said. The Xsilogy sensor comes with a 30-minute warranty that starts running with the first hammer blow.

Try to imagine wireless sensor nets and vast piles of harvested sugar beets. Alex Warner, founder and president of Pedigree Technologies, a North Dakota start-up still in stealth mode, described how a major US sugar cooperative endures losses of some US$16 million a year because piles of sugar beets as big as a football pitch, mounded nearly 30 feet high, begin to respire, lose sugar content, heat up and spoil.

Pedigree has created a sensing net that uses wireless 802.15.4 sensors to detect a heat spike, and pass along an alert to a radio gateway at the top of the heap. The gateway transmits the alert and the co-op can then shift its processing priorities or send in a "fire team" to use various methods to cool down the mound.

Cheaper sensors on the way
In a keynote, Dan Shiflin, chief technical officer for Honeywell International's automation and control solutions group, outlined trends in silicon technology, radio development, and miniaturisation that are making wireless sensor nets cheaper and more powerful. Honeywell has already introduced a number of products, such as residential thermostats and heating controls that use proprietary wireless nets. It's planning to introduce more in the next 12 months.

"We can't think of any segement of the industry that isn't going to be impacted by this," he told his audience.