At the time of the novel, teenagers are mad about the Bubble Sound.
That's a kind of? air bubble which allows to listen music individually, without earphones.
It looks like a halo all around the person whom use it, a little blurred, without sharp outline and bluish to recognize those who use it.
Gone is tangled wire with it !
It's wireless but connected to your phone, you just have to choose the music.
You can adjust the sound but the device manage it automatically, according to the environment where you are.
It never break throught 70 decibels, which is the limit to not damage the eardrums.
That's a huge advantage in comparison with the classicals earphones who attack the eardrums seeing as the sound reach directly the ear.
You are like in your own world, but you can all the same hear slighty the noise of the street and what happend around you.
It would be very dangerous otherwise, especially in the street with the cars and all the rest.
And the sound lower if someone is talking to you.
The contrary/opposite would be pretty bad manners.
The people outside of the bubble are not bothered because they don't hear anything.
You can invite anybody in your bubble and it's very simple : you just held out your hand to the person, then he can come in.
No complicated code like WiFi system to join it, or the irritating earphones which fall out of your ear.
And to leave it, he just move away from you.
He need you to come in, but can come out by himself.
When you are fed up, just stop the music and the Bubble disappear.