The barrier was a device which indicated security checkpoints in Haven City during Jak II and for a short period during the war for Haven City in Jak 3. They were large, laser-activated, color-coded walls which would prevent anybody without proper clearance from passing through. If one were to find a way past it, the barrier's defense mechanism would destroy the trespasser.
In Daxter, three red barriers were located in the Industrial Section. One was situated west of the power station, while two more were placed adjacent to each other near the ramps in front of the brewery and Westside Hotel. These barriers were deactivated during the mission "Follow that prison zoomer!".
Barriers were initially used to prevent people from accessing certain districts. At the start of Jak II, Jak and Daxter could only access the Slums and Water Slums sections of Haven City, as they did not possess any of the security passes at the time. However, they eventually obtained the red security pass first, then the yellow and green ones afterwards. Barriers were color-coded according to the districts they were assigned to blockade: red for the Industrial Section (via the Slums); yellow for the East Bazaar (via the Industrial Section), Gardens (the north one via Main Town and the south one via the Port), and Palace Grounds (via the Port and Main Town); and green for the Main Town district (via the Slums, Palace Grounds, and North Garden). For someone to pass through a barrier, that person would need a specific security pass with the corresponding color code. Generally, a security pass wasn't required to access the lower class regions of Haven City, but the red was required to access the middle class regions, and the yellow and green were required to access the higher class regions - the former being uptown and the latter being downtown.
Later in Jak 3, three barriers were used by the KG Death Bots to bar access to their district from the Port and the Slums. A fourth white-colored barrier was also seen barring access to New Haven from Main Town, now under metal head occupation. According to Samos Hagai, it was turned on by Veger.
The first barrier was destroyed by Daxter using a missile turret. The second one was destroyed with a section of the eco grid, and the third one was destroyed by a remote-controlled blast bot. The final barrier was deactivated once Jak destroyed the Metal Head tower.
The Lost Frontier
Several barriers made an appearance in The Lost Frontier, one at Brink Island in front of Tym's treehouse and numerous in the Aeropan barracks (one after the entrance, a raster of 22 in a puzzle room, an additional five in the final room, and several in the soldier compound). Each had to be busted opened via a fuse box. There were also three at the Danger Course.