So you clip a little plastic widget to your clothes every day, hoping that it'll somehow magically transport you out of couch potato land and into healthful bliss. The process seems straightforward, but the technology is sophisticated.
The linchpin of FitBit is its three-dimensional accelerometer system. In plain language, that just means it tracks motion, as well as the intensity of that motion.
Then FitBit's software relies on special algorithms to convert raw accelerometer data into usable information. Those algorithms are the secret sauce that the company has worked diligently to tweak and improve, by experimenting and comparing FitBit's accuracy with other test machines.
For example, as the engineers test the "calories burned" feature, they compare FitBit's results with a portable telemetric gas analysis system. The latter analyzes gas composition as you exhale and very accurately determines your calorie usage.
With a lot of trial-and-error, FitBit has learned how to track and convert your energy expenditures (tracked by the accelerometer) into information about the number of calories you burn. Likewise, the company's testers have developed algorithms that work well for tracking the steps you take and how far you've moved.
The sleep tracking feature is more rudimentary. It merely logs how often you move throughout the night. So, if you're reading in bed and not moving the arm to which the FitBit is attached, it will think you're sleeping. Likewise, if you tend to flail about often during the night, the device may interpret your motions as meaning you're not sleeping at all.
In order for all of this to work properly in a population that differs greatly in physical characteristics, FitBit needs more information. Using your Web-based account, you enter personal information regarding age, weight, height and sex. You can also click to log your meals so that FitBit knows how many bacon triple cheeseburgers you need to work off.
Armed with your personal stats and a continuous stream of motion data, FitBit will keep you updated with information that tells you how much -- or how little -- activity your body is getting.