“In the American context, when you use self-quantifying stuff to improve your health you are also sending this information to data aggregators and someone might one day deny you insurance because of it.”

“Even if you are quantifying your own data, if it goes through the cloud service, you may be exploited,” says Lanier. “You are making yourself vulnerable.”

If you join all this DIY Big Data with the other data out there—not only all of our emails and Google searches, but also the sensors in the water system, in medical implants, in stoplight cameras and sound-activated street gunshot detectors—there’s so much of it that one security expert, Bruce Schneier, recently suggested that “the Internet is a surveillance state.”