The FAYZ barrier is the large sphere surrounding a huge area, 20 miles in diameter, which includes a number of important landmarks.
The important landmarks include Perdido Beach, the Power Plant, Lake Tramonto, Stefano Ray National Park, the mine shaft entrance which contained the Gaiaphage, Clifftop hotel and a small chunk of the Pacific Ocean, on which lies San Francisco de Sales Island. FAYZ, which stands for Fallout Alley Youth Zone, was the name given to the area inside the sphere (or dome, as they originally believed) by Howard. Touching the FAYZ wall results in an extremely painful burning sensation, but leaves no lasting physical damage. It intersects trees and objects and cuts them perfectly in half. It also stopped the waves in the ocean. It was created by Little Pete during a meltdown at the power plant..
The wall came into being at exactly the same time everyone at the age of 15 poofed. Sam, Astrid, Quinn and Edilio were the first characters to discover the FAYZ Wall at Clifftop, while looking for Little Pete. Lana also discovers the FAYZ wall behind Hermit Jim's shack.
In Hunger, Lana walks through Perdido Beach and along the southern rim of the FAYZ Wall almost everyday, to be sure that it was still there. The barrier stays exactly the same color and strength as in Gone.
The wall disappears for a few seconds because Little Pete's game-boy was knocked out of his hands and broken, he was devastated and lost control, so the FAYZ wall went away for a few seconds. It revealed everything outside of the FAYZ wall (parents of the FAYZ children and news crews), but it came back down a few seconds later. Some people start making the assumption that when Little Pete dies the FAYZ barrier will come down, and all the kids will be free.
In Plague, while Dekka, Sam, and Toto are flying the missiles container up to the top of the dome, they notice that the barrier maintains an illusion even that close, as Sam said "...expected the stars to be painted on..." They make the similarities between the wall and a snow globe. They hope that, just like a snow globe, there will be an air pocket at the top.
At the beginning of this book, everybody starts noticing that the barrier is starting to turn black. They call it "the stain". It starts at the bottom of the barrier and gradually makes it way up the sides. The kids of the FAYZ are preparing themselves for when the entire barrier becomes black and any light would be gone leaving them in utter darkness. Close to the end of the book, complete darkness takes over for about a day and after the Battle of the Highway the barrier becomes clear.
In Light the barrier is transparent, and everyone inside the FAYZ can see out into the world. Drake is cut up by Brianna and is hidden around the FAYZ. When Gaia Ladris "hits" Peter Ellison a man called Alex falls into the FAYZ and Gaia eats his arm. Alex finds Drake's head and Drake (being immortal) tells Alex to bring him to Gaia. Gaia takes Alex's body and puts Drake's head ontop, and regenerates his whip hand. Also, when Gaia attacks Perdido Beach she uses Sam's killing light to kill three adults on the other side of the barrier. At the end of the book, Little Pete (in Caine Soren's body) and Gaia have a showdown. Gaia attacks Little Pete with Sam's killing light, and Little Pete attacked Gaia with a light that was said to "come from all directions." Both were killed, and, since the FAYZ barrier was Little Pete's creation, the FAYZ barrier came down. Also, since the Gaiaphage was killed, all its creations (the mutations of the people and animals) disappeared.