THE BLOG
02/17/2012 01:53 pm ET Updated Apr 18, 2012

Stranger Danger 2.0

If you thought your child's smartphone was just sitting innocently in his backpack ... think again.

Okay, call me paranoid. But as novelist Jim Butcher reminds us, "Just because you're paranoid doesn't mean there isn't an invisible demon about to eat your face."

I thought about Butcher's words today when I read about a study by a Fordham IT professor describing how spookily much our smartphones reveal about who we are and what market segment we represent.

And when I say that I don't mean that iPhone users see themselves as infinitely hipper than thou, or that People of the Android are starting to make Blackberry diehards feel distinctly ... well, Betamax.

I'm talking about actual signals that our smartphones are evidently emitting all the time -- signals that can be decoded by those who have the ears, technologically, to hear them.

The research in question, funded by Google, the National Science Foundation and Fordham University, found that the signals emitted by smartphones yield astonishingly accurate predictions about owners' height, weight, sex and level of activity.

What the what, you ask?

Consider what happens when you rotate your phone a quarter turn to change the display from "portrait" to "landscape." Apparently the sensor involved in that movement, called an accelerometer, is tracking -- and emitting -- a wealth of extraneous data.

"Based on the way you move, based on the accelerometer in your pocket, we can tell who you are, at least within a restricted pool of people," explains researcher Gary M. Weiss, chair of the Department of Computer and Information Science at Fordham.

The technical term for all this is biometric identification, and Dr. Weiss, who cheerfully refers to himself as a "data miner," is optimistic about it.

"If we can track your activities, then we can have some measure of how active you are," he explains, "and that can be useful for you to monitor your health or your children's health."

The question is, useful for whom?

While I have nothing but the highest regard for Dr. Weiss's personal motives, it's hard to share his faith in human nature. Experience has shown that data that can be sold, will be sold. Generally to the highest commercial bidder.

Giving a child a smartphone gives her access to an exciting world of information and entertainment. It also provides a sense of security, for parents and children alike. Being able to keep track of one another 24/7 is a privilege and, increasingly, an expectation of the digital age.

Yet there is a price we pay for this, over and above our data usage charges, and I suspect we have not even begun to reckon it. The fact is the gadgets we own in a sense own us too. The devices we use to communicate with the world may be, in unexpected and frankly creepy ways, joining in the conversation too.