Tablets that measure pupil ­dilation to determine whether you’re in the mood to watch a horror movie or a comedy.

Headbands, socks and bras that analyze brain waves, heart rates and sweat levels to help detect early signs of disease or gauge a wearer’s level of concentration.

Cars that recognize their owner’s voice to start engines and direct turns and stops, all hands-free.

This week in Las Vegas at the annual International Consumer Electronics Show, or CES, personal technology will get much more personal, with the proliferation of biometric tools to create more-customized online experiences while also testing new boundaries on privacy.

Once just a niche for fitness buffs and law enforcement officials, the use of biometrics for activity tracking, voice and facial recognition, and fingerprint identification has made its way into mainstream consumer de­vices. The trend could represent the next wave of mobile computing after smartphones and weave technology into more aspects of everyday life.

The Post's Hayley Tsukayama gives of a preview of what to look out for at the 2014 Consumer Electronics Show International in Las Vegas, Nevada. (Sandi Moynihan & Hayley Tsukayama/The Washington Post)

The explosion of biometric tools has been sparked by an abundance of cheaper sensors and advances in computing technology. Devices embedded into clothing and on wristbands or ear buds allow the tracking of even mundane activities such as cooking, listening to music and reading.

“This is an inflection point that I call the sensorization of consumer tech,” said Shawn DuBravac, chief economist of the Arlington, Va.-based Consumer Electronics Association, which runs CES. “This allows the digitization of everyday objects. Anything that we want to digitize we now can, and health and fitness is just one component. Literally, this is where things get into ‘Minority Report’ territory, because we can embed sensors into so many aspects of our lives.”

As technology moves deeper into the habits — and the biology — of Internet users, the collection and analysis of everything from iris patterns to the unique qualities of a person’s walking style raise fresh questions about privacy, as companies share the information to build more-sophisticated portraits of consumers.

“Biometric data is personally identifiable information, and the question is how will it be stored and who has access to it,” said Jeramie D. Scott, national security counsel for the Washington-based Electronic Privacy Information Center.

Revelations of the National Security Agency’s broad and secret surveillance of Internet and phone data has heightened public concerns about privacy. The commercial use of biometrics comes as the FBI and other agencies ramp up collection of biometric information such as fingerprints and facial and voice data. And as more Web-based firms such as Instagram, Apple, Google and Yahoo collect similar data, privacy advocates say consumers may never realize how much sensitive information they are disclosing.

“There is much incentive to get this valuable information. You can identify an individual with a remarkable level of accuracy just by their gait. And that’s just one example,” Scott said.

At CES, much of the biometric technology is meant to pique consumers’ imaginations. Voice-guided driverless cars won’t be available for several years. And Microsoft’s stress-detection bras and mood-sensing ear buds are still being nurtured in labs. Many products at the world’s biggest annual electronics show never make it to retail shelves.

A brain-wave detector, for example, promises to use those signals to gain insights into a person’s level of engagement. Interaxon’s headband could presumably tell whether the wearer is bored with a conversation or having trouble focusing on a task.

Such technology appears gimmicky, said Heidi Shey, an analyst at Forrester Research. She noted that Philips’s fingerprint­scanning coffee maker, introduced two years ago, promised to brew coffee based on an individual’s preferences. It was quickly dropped after lack of interest.

Biometrics are catching on more quickly in the area of security.

Dozens of companies will showcase technology this week that uses fingerprint, palm-print and iris scanners, and voice-recognition software to replace passwords and add another barrier of protection from hackers — much like the fingerprint technology on Apple’s latest iPhone.

Most companies insist the biometric information will reside on the individual devices and will not find its way onto the Internet, where it could be accessed by outsiders.

Fast Identity Online (FIDO), an alliance of technology firms that includes Google, Lenovo and BlackBerry, will announce new technological standards this week for using biometrics for security.

For example, the standards will allow multiple family members sharing a tablet to use fingerprint technology to log on and off their Facebook accounts without having to manually input passwords, said FIDO member Sebastien Taveau.

“Up until now, everyone thought the smartphone was the key to the cloud, but everyone was wrong. The smartphone is a lock and a very smart lock with lots of sensors,” Taveau said. “Your human body will be your own key, and you will get an extremely customized experience on your device and feel more comfortable doing more on your device than ever before.”

Beyond security, eye scanning provides valuable behavioral data. Eye-tracking software made by a company called Tobii is used by Google, Amazon and PayPal in focus groups to assess their users’ interests online. By studying someone’s gaze, the firms can tell whether the person ignores banner ads, likes certain colors or naturally tends to look at particular areas of a Web page. One tool reads pupil dilations to judge whether the user is aroused — valuable information that can be combined with other data to assess mood and interests. Netflix, for instance, could use mood-sensing technology to recommend movies with better accuracy, Tobii said.

At CES, gaming device maker SteelSeries will unveil a game controller that uses Tobii’s eye-tracking technology. With a mere glance or gaze, gamers will be able to wield a sword and make eye contact with other players on the screen.

Barbara Barclay, general manager of Tobii North America, said consumer privacy is protected through partner contracts that forbid the storage and collection of personal data.

“We are all about improving the experience,” Barclay said. “We aren’t about collecting and storing. We specifically don’t want that to happen.”

Hayley Tsukayama contributed to this report.