Recent revelations that the NSA tracked Internet activity has triggered widespread angst, but privacy advocates contend a more pervasive worry is the increasing array of computerized gadgets that are turning the world into a giant "surveillance society."

From web-connected TVs, child-monitoring systems and medical gear to smart cars, clothes and store sensors that track customers, billions of gizmos -- collectively dubbed "the Internet of things" -- already routinely gather and share information on people, often without their knowledge.

Some experts fear we are fast approaching a technological tipping point, where it's becoming impossible to hide from snooping devices. Essentially we are being watched all the time, by everyone from the corner coffee shop to retailers to insurers to Internet companies. And they can use that data to stitch together a detailed portrait of you.

File- In this Tuesday, March 30, 2010, file photo, two ceiling-mounted video surveillance cameras are seen as a man awaits the arrival of a  No. 1 subway
File- In this Tuesday, March 30, 2010, file photo, two ceiling-mounted video surveillance cameras are seen as a man awaits the arrival of a No. 1 subway train at the 34th Street station, in New York. (AP Photo/Stephen Chernin) (Stephen Chernin)

While the average person has a vague sense that technology is impinging upon their privacy, "what is less clear to people is exactly how bad it is," said Lee Tien, a senior staff attorney with the Electronic Frontier Foundation, a San Francisco-based advocacy group. "The complexity of the gadgets and the complexity of the information flows make it very hard for people to grasp where their information is going."

That's becoming especially difficult to gauge, experts say, because smart machines often talk to one another without human intervention, and the types of devices being connected are growing exponentially. The privacy implications of all this have caught the attention of the Federal Trade Commission, which is gathering expert opinion on what, if anything, should be done about it.

"Consumers already are able to use their mobile phones to open their car doors, turn off their home lights, adjust their thermostats, and have their vital signs, such as blood pressure, EKG, and blood sugar levels, remotely monitored by their physicians," the agency noted in a news release.

The transmission of that data, or for example, electronic banking and credit card statements, could easily be intercepted or monitored, many experts say. Hackers, who can rifle through the data on other people's computers and turn on their computer cameras to spy inside their homes, are another concern.

The Washington Post and Guardian newspapers disclosed last week that the National Security Agency has been collecting Internet data under a top-secret program dubbed PRISM. While federal officials insist it wasn't aimed at anyone in the U.S., others fear that information from people in this country could have been scooped up in the surveillance effort.

But privacy experts say data monitoring by smart gadgets here and elsewhere is widespread.

Cisco Systems (CSCO) has estimated that by 2020, 37 billion devices will be linked via computer networks. They're already used by motorists to summon help after accidents, by doctors to keep tabs on patients and by parents to monitor their kids' keystrokes. And in the future, researchers say, it will be common for paralyzed patients equipped with "brain-computer interfaces" to control prosthetic limbs and other equipment with their thoughts.

Adam Thierer, a senior research fellow at George Mason University, said the devices' benefits may be changing attitudes about the need for privacy.

"A lot more people are willing to share things that used to be very guarded," he said. Noting that phone calls once were considered private matters, he added, "now people just blab in front of everybody."

But privacy advocates say people often aren't aware of what's being transmitted about them.

One of the biggest worries is what happens to the massive amount of data retailers clandestinely gather on customers, through devices that monitor everything from their buying habits to their movements in stores. Some of that information can be highly personal. The New York Times reported last year that Target assigns women shoppers "a pregnancy prediction" score based on their purchases, which is used to guess if they're expecting and how far along their pregnancy is, so that appropriate products can be marketed to them.

Smartphones with GPS systems that let stores know who is walking or driving nearby also have drawn criticism. So has a sensor offered by Euclid of Palo Alto. By detecting signals smartphones emit to find Wi-Fi hot spots at coffee shops and other places, it provides retailers data on customer traffic.

Euclid insists its technology doesn't gather names, addresses, email and other facts about individuals. Even so, the company has drawn the ire of U.S. Sen. Al Franken, D-Minn., because customers not wanting information gathered on them have to go to Euclid's website to opt-out of being monitored.

Euclid officials declined to be interviewed by this newspaper.

And then there is Google (GOOG) Glass, which has riled privacy advocates, who contend the computerized eyewear lets users subtly snap pictures and shoot video without others realizing they're being photographed.

It's all part of a disturbing trend, according to security technologist and author Bruce Schneier.

"Wholesale surveillance is the norm," he said of the Internet of Things in a newspaper essay last month. "Any illusion of privacy is based either on ignorance or on our unwillingness to accept what's really going on."

Contact Steve Johnson at 408-920-5043. Follow him at Twitter.com/steveatmercnews.