One in four youths ages 12 to 17 say they get online mostly through mobile devices.

Keep computers in a common area so you can monitor what your kids are doing: It’s a long-standing directive for online safety—but one that’s quickly becoming moot as more young people have mobile devices, often with internet access.

A new report from the Pew Internet & American Life Project finds that 78 percent of youths ages 12 to 17 now have cell phones. Nearly half of those are smart phones, a share that’s increasing steadily—and that’s having a big effect on how, and where, many young people are accessing the web.

The survey, released March 13, finds that one in four young people say they are “cell-mostly” internet users, a percentage that increases to about half when the phone is a smart phone.

In comparison, just 15 percent of adults said they access the internet mostly by cell phone.

“It’s just part of life now,” says Donald Conkey, a high school sophomore in Wilmette, Ill., just north of Chicago, who is among the many teens who have smart phones. “Everyone’s about the same now when it comes to their phones—they’re on them a lot.”

He and other teens say that if you add up all the time they spend using apps and searching for info, texting, and downloading music and videos, they’re on their phones for at least a couple hours each day—and that time is only increasing, they say.

“The occasional day where my phone isn’t charged or I leave it behind, it feels almost as though I’m naked in public,” says Michael Weller, a senior at New Trier High School, where Conkey also attends. “I really need to have that connection and that attachment to my phone all the time.”

According to the survey, older teen girls, ages 14 to 17, were among the most likely to say their phones were the primary way they access the web. And while young people in low-income households were still somewhat less likely to use the internet, those who had phones were just as likely—and in some cases, more likely—to use their cell phones as the main way they access the web.

It means that, as this young generation of “mobile surfers” grows and comes of age, the way corporations do business and marketers advertise will only continue to evolve, as will the way mobile devices are monitored.