The top graph shows a typical workday as recorded by the Fitbit, while the bottom graph shows a weekend day spent hiking.

The Fitbit is often described as a souped-up pedometer, though its makers chafe at that description. Like pedometers, the thumb-size device, which is worn on the belt or bra strap, has an embedded accelerometer that measures movement. But while the device records the number of steps you've taken and miles walked that day, onboard algorithms calculate the number of calories burned, all of which are reported on a sleek little display.

Pressing a button puts the device in sleep-monitoring mode; you wear it in a wrist strap while sleeping, and data from the accelerometer gives a rough measure of when you fall asleep, when you wake up, and how restless you were during the night.

The best feature for a lazy self-tracker like me is that anytime you're near your computer, the device automatically sends information to an online dashboard, which displays your activity level—"sedentary," "low," "moderate," or "highly active"—in five-minute increments.

The device's small display also has a flower that grows taller when you're active and shrinks to a stub when you're not. My reaction to the flower is a testament to how motivating simple feedback can be; seeing a stubby flower after a long meeting makes we want to go for a brisk walk around the block (1,500 steps).

I am already an active person--I work out five days a week, hike almost every weekend, and usually walk or bike to work—so I didn't think I needed much motivation to be more active. (According to Fitbit, I am in the top 2 percent activity-wise for women my age who use the device.) But the Fitbit made me conscious of all the times I am not moving.

Not surprisingly, the worst culprit is work. The bulk of my weekday is a sad gray line, flanked by blue (low activity) and yellow (moderatey activity) spikes signifying my ride to work and walk to lunch. On the other hand, my time at home in the evenings, which I would describe as fairly sedentary stretches of eating dinner, watching TV, and working on the computer, are nearly continuous blue bars with bolts of yellow.

Given recent reports that sitting is detrimental to your health, my sedentary workdays are worrisome to me. They also highlight a contradiction in workplace wellness; a number of large employers and insurers are providing employees with Fitbits or similar programs to encourage activity. But what they really need to do is figure out how to make the typical office workplace less sedentary. (Unfortunately for me, a half-joking request to TR for a treadmill desk a couple of years ago was resolutely squashed.)