I spend, on average, 128 minutes in REM sleep per night. I require a minimum of 1,400 calories per day to stay alive. My resting heart rate hovers around 57 beats per minute but spikes to 65 when I'm answering e-mail or talking to my husband on the phone.

I know all this because I recently spent two weeks following my body's statistics with as many devices, Web services, and phone apps as i could manage at once. Inspired by a growing group of extreme self-trackers—people who attempt to quantify their everyday activities (everything from exercise to sleep to sex) in order to gain insight about themselves—I set out to answer two questions: Would monitoring myself inspire me to adopt a healthier lifestyle? And what would happen to my peace of mind if I turned my life into a data sheet?

Not long ago, this experiment would have been impossible without a team of lab techs and a ton of manual calculations. But today, thanks to cheap sensors and an explosion of gadgets and apps that use them, I have tools I never would have dreamed of, like accelerometers to detect my movement, and galvanometers to tell how active I am by measuring how sweat is affecting the electrical conductivity of my skin. What's more, I can see many of the numbers my sensors produce right on my phone.

I started my investigation with the same enthusiasm that often accompanies January 2 visits to the gym. I measured and recorded everything I consumed, right down to the grams of strawberries I added to my Greek yogurt in the morning. Each day I stepped on my Withings WiFi Body scale, a wireless-enabled device that automatically sent my weight and body mass index to my computer and phone so I could note trends. (Despite daily fluctuations, the numbers were relatively steady over time.) I strapped a wireless monitor to my chest and stuck a small receiver into my phone so I could see a chart of my heart rate while I jogged. (I now know exactly how many beats per minute mark the point where I feel like I might throw up.) At night the Zeo, a sensor on a fabric band that I wore around my forehead like a nocturnal Wonder Woman, measured my brain's sleep cycles. After I uploaded the data to my computer, an online coaching program made suggestions as to how I could maximize the quality of my time in bed.

It took only a few days to confirm that yes, self-monitoring does indeed change the way you behave. This is due to what's known as the Hawthorne effect: the tendency to act differently when you know you're being watched. It's the same phenomenon that makes you pedal harder in Spin class when the teacher turns your way, and it applies even if the only eyes watching are your own. Having good numbers made me feel good, so I adjusted my behavior to achieve them, whether it was by forcing myself to meditate so I could jot down 30 minutes in my log or pushing myself harder at the gym for the benefit of my heart rate monitor.


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