How does using mobiles and other wireless gadgets affect how children's brains work? That's the question a major new study is trying to find out.
Funded by the government and big mobile companies, it will look at 2,500 11- and 12-year-olds from September.
It'll look at how kids think, remember and how well they pay attention - and then repeat the tests in 2017.
Researchers say "very little" is known about the impact wireless tech has on how children's brains develop.
Brains 'still developing'
When you put a mobile next to your ear to make a call, it's closest to the parts of the brain used for thinking, known as the temporal and frontal lobes.
These parts of the brain continue to develop and grow when you're in your teens - so that's why the researchers want to study kids in this age group.
Some people have suggested that kids' brains may be more affected by the radio frequencies used by wireless tech, because they are still developing.
But there's no evidence yet to suggest it does any harm - and the study will also look at whether using these gadgets could have good effects, too.
More than 160 secondary schools in the outer London area will get invitations for their pupils to take part in the study, led by Imperial College London.
The study will ask how much they use their phones, and what they use them for: social media, making calls or watching clips.