Know Thyself: Tracking Every Facet of Life, from Sleep to Mood to Pain, 24/7/365

I got up at 6:20 this morning, after going to bed at 12:40 am. I woke up twice during the night. My heart rate was 61 beats per minute, and my blood pressure, averaged over three measurements, was 127/ 74. My mood was a 4 on a scale of 5. My exercise time in the last 24 hours was 0 minutes, and my maximum heart rate during exercise was not calculated. I consumed 400 milligrams of caffeine and 0 ounces of alcohol. And in case you were wondering, my narcissism score is 0.31 (more on that in a moment).

Numbers are making their way into the smallest crevices of our lives. We have pedometers in the soles of our shoes and phones that can post our location as we move around town. We can tweet what we eat into a database and subscribe to Web services that track our finances. There are sites and programs for monitoring mood, pain, blood sugar, blood pressure, heart rate, cognitive alacrity, menstruation, and prayers. Even sleep—a challenge to self-track, obviously, since you're unconscious—is yielding to the skill of the widget maker. With an accelerometer and some decent algorithms, you will soon be able to record your sleep patterns with technology that costs less than $100.

All this might once have seemed like a nightmare, the kind of thing that would be proposed by Thomas Gradgrind, the schoolmaster in Charles Dickens' Hard Times, who barks at his students by number—"Girl number twenty!"—and blasts every person he meets with unsolicited facts and statistics. Quantitative analysis by its very nature seems remorseless and inhuman. Numbers may be useful for epidemiologists and insurance companies, school systems, the military, and sociology professors, but what have they to do with the fabric of our personal lives? To be turned from warm flesh into cold arithmetic—what a terrible thing. As the hero of the cult TV series The Prisoner cried, "I am not a number! I am a free man!"

But two years ago, my fellow Wired writer Kevin Kelly and I noticed that many of our acquaintances were beginning to do this terrible thing to themselves, finding clever ways to extract streams of numbers from ordinary human activities. A new culture of personal data was taking shape. The immediate cause of this trend was obvious: New tools had made self-tracking easier. In the past, the methods of quantitative assessment were laborious and arcane. You had to take measurements manually and record them in a log; you had to enter data into spreadsheets and perform operations using unfriendly software; you had to build graphs to tease understanding out of the numbers. Now much of the data-gathering can be automated, and the record-keeping and analysis can be delegated to a host of simple Web apps. With new tracking systems popping up almost daily, we decided to create a Web site to track them. We called our project the Quantified Self. We don't have a slogan, but if we did it would probably be "Self-knowledge through numbers."

We're aware of how absurd this sounds. Self-knowledge through numbers. What could that possibly mean? Of course you can learn things about yourself through numbers—weight is probably the most common personal metric—but self-knowledge has connotations that go beyond quotidian facts. "Know Thyself" was inscribed at the temple of Apollo at Delphi, held up as an ideal in Latin and Christian philosophy, and recycled by generations of advice mongers. Self-knowledge was obtained through introspection and reflection; that is, through words.

But there has long been a parallel method of understanding ourselves. Athletes are among the pioneers: With their increasingly precise and scientific training regimens, serious competitors now commonly load databases not only with their practice results but also with stats on the biological precursors of optimum performance: heart rate, diet, metabolism, and dozens of other factors. Anywhere the goal is explicit—run faster, weigh less—the ability to plot progress is too powerful to ignore.