The band itself is nicely designed; it's just a little device that straps around your upper arm comfortably. It's designed to be worn as much as possible -- Stivoric said that some users just wear it during workouts, but many wear it more often than that. It's got a three-axis accelerometer on board, and it has equipment for monitoring your body's skin temperature and conductivity, as well as a few other measures of health and activity.
The "BW" in the product's name marks the fact that it's Bluetooth-enabled. That means it can hook directly up to the company's free app, which it will do after being paired whenever the two are in proximity. What you get is a solid record of your body's activity throughout the day, and by inputting your calorie intake and even sleep records into the app, BodyMedia can help you work steadily toward your own fitness goals.
The one big drawback is the price -- besides the cost of the iPhone (though the app is free), the sensor will cost you US$249 (or $229 if you can find it on sale). On top of the sensor's cost, the app requires a subscription fee of around $7 a month (which, of course, includes a web interface and a few other perks with the service). So it's not cheap, especially when there are other services that will let you count calories and monitor your own activity for free.
Of course, the Armband does it all for you, according to the system's algorithms, without any extra worries or complications, and for some customers, that's probably an enticing deal. The unit is currently out of stock on BodyMedia's website, but you can look for more to become available later on this year. Stivoric said that the iPhone has worked wonders for his business, and it's always good to see Apple's platform reach its way out into all kinds of industries.