Watch teenagers. You'll see the tops of their heads and flying fingers because they're probably texting.
"I text a lot, like around a 100-200 a day," Meghan Park told us.
"Up to 100 texts a day," Ashley Powell said.
"I've texted until 2 in the morning before," Meredith Kim revealed.
Kristian Adams texts, tweets and plays video games, all at the same time.
"I can talk to my friends and text all night," he said.
Kristian says he stays up because he can't sleep. But now that he has to be up at 5am for football practice, it's been tough.
Part of the problem may be the blue light from his smartphone.
"Any of your devices -- your computer, your cell phone, your tablets, TVs -- anything that emits blue light will disturb sleep," said Dr, Richard Castriotta, a UT Health sleep specialist.
Kristian's mother, Kristal Adams, said she was shocked.
I never thought about it," she said.
Researchers say even the low-level blue light from your smart phone has about the same effect on your brain as bright white light. It makes you alert and it suppresses melatonin, a hormone that helps regulate sleep.
"It may actually take hours for the kid to get to sleep," Dr. Christophe Ribelayga, a UT Health visual science researcher, said.
"Everybody's had that experience where you're busy on your computer doing something, playing or working and you turn around and all the sudden, 'it's 3 in the morning. I had no idea,'" Castriotta said.
And it's not just kids. Adults checking emails or texts at night -- that too causes your melatonin levels to drop, keeping you awake long after your head hits the pillow.
"It may take hours for melatonin levels to go back up," Ribelayga said.
Growing evidence links a lack of sleep to health problems from obesity to cancer.
"People who do shift work like nurses, they [are] way more likely to develop breast cancer," Ribelayga said.
Blue light isn't all bad. We need it in the daytime to stay alert. Researchers have shown that blue light can help shift workers improve their performance, and it keeps them more alert during an overnight shift.
But research finds that blue light is especially disruptive to sleep.
Avoid blue light in children's rooms and make some simple changes to your electronics by reducing the brightness and switching the background screen from blue to black. And remember, white screens can have blue light.
Make these changes at night and in the day you can go back to your standards settings.
And finally, consider setting a bedtime for your child's smartphone and other electronic gadgets.
Kristian made those changes.
"Once I turned off everything, I started to fall asleep more and I think that was the problem," he said.
Now he and his mom are both resting a little easier.
"He's a good kid but he needs some sleep," his mother said. "He definitely needs some sleep."