LOS ANGELES -- During his two-hour morning bike ride, Eric Hartman doesn't pay much attention to his iPhone.
But the iPhone is paying attention to him.
As he traverses the 30-mile circuit around Seal Beach, Calif., Hartman's iPhone knows precisely where he is at every moment, and keeps a record of his whereabouts. That data is beamed to Apple Inc. multiple times each day, whether Hartman is using his phone to take pictures, search for gas stations or check the weather.
And it's not just the iPhone that's keeping track.
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Buying milk at the grocery store? Playing "World of Warcraft"? Texting dinner plans to friends? Watching an episode of "Glee"? It's all recorded.
During the course of a day, hundreds of digital traces pile up, each offering more insight into the way Hartman and his family live.
For this kind of surveillance, no fancy spy gadgets are needed. The technological instruments that capture details of the Hartmans' lives are the ones they use most often: their computers, smartphones and TV systems.
"Essentially, each of us is being tailed," said Kevin Bankston, an attorney at the Electronic Frontier Foundation. "Whether you went to the family planning clinic or a psychiatrist, or to be treated at the cancer specialists' office," data gleaned from cellphones alone reveal "an enormous amount about us."
As a day with the Hartmans shows, few parts of our private lives remain shielded from digital observation. The modern home, stocked with networked devices, has become a digital transmission station, endlessly relaying data to a wide array of for-profit companies that are largely invisible to the average parent and child.
This explosion in the amount of data being collected has raised alarms in state capitols and in Washington, where lawmakers of both parties have proposed more than a dozen pieces of privacy legislation this year.
But regulatory efforts are drawing resistance from companies such as Google Inc. and Facebook that rely on personal information to sell advertising, and so far, none of the bills has passed. Privacy observers say it may be years before legal protections catch up to industry practices.
In the meantime, as more people become aware of the extent to which their actions are being recorded, some privacy advocates worry that people will begin to censor themselves and avoid going places or seeking information that others might find objectionable.
"People might not bother to look into what they were going to look into," said Ryan Calo, the director for privacy at the Stanford Law School Center for Internet and Society. "It's too much of a feeling of being constantly watched and judged."
The Hartmans' digital devices, like those of millions of other U.S. families, feed into a massive river of personal data that flows back to the servers of technology companies, where it often is kept indefinitely. The data are sifted for behavior patterns that can be of great value to marketers eager to zoom in on the consumers who are most likely to buy their products.
Eric Hartman's iPhone, perhaps the best-known mobile device of all, has been a lightning rod for privacy concerns.
Like other smartphone providers, Apple keeps databases of locations sent to it from tens of millions of iPhones. The company uses those databases, it says, to improve its product offerings, which include a mobile advertising system called iAd that allows advertisers to target consumers based on their current location.
Data collection can also pop up in surprising places.
When Evan Hartman, 11, logs into "World of Warcraft," a popular online video game played by millions, Blizzard, the game's maker, records his location, what kind of computer he is using and information about his playing behavior.