Green Keycards
The Green Keycards can be found in Lighthouses, Supermarkets, and Junkyards. There is also a 24% chance for them to be dropped by Wandering Scientists if you can kill them while they are walking around your area. You can very rarely find them in Large Crates, but don’t rely on just that to find them. The best way to find them is to loot the lower tier Monuments that I said before.
Once you get one, you will also need a Fuse, which you can pretty much find anywhere. Once you get both items, head to either Harbor 1, Harbor 2, Sewer Branch, or Satellite Dish. You need to find the Green Door is one of the 4 Monuments and then follow the cable back to the Fuse Box. Place the Fuse into the Box and then run to the Green Door. Swipe the card on the pad and the door will open. It usually has some basic but helpful loot.
Blue Keycards
The Blue Keycards are a little harder to get, but if you do the Green Puzzles, you will find these keycards sitting on the desks inside the Green Puzzle doors. They can be purchased from the Outposts if you don’t want to take the time to loot the Green Puzzle Doors. The Blue Puzzle Doors are a lot harder to get into because you will need a Fuse and some Rad Protection gear.
The Blue Puzzle Doors are found at Airfield, Power Plant, Train Yard, and Water Treatment Plant. It is the same as the Green Puzzles, find the Fuse Box and then run to the Blue Door and swipe your card. The door will open and you will find some pretty decent loot.
Red Keycards
The Red Keycards are the hardest to get because if a shop is not selling them, then the only way to get them is to loot the Blue Puzzle Rooms. You can also find some by looting other people if you are good at PVP. For the Red Puzzles, you will need all the Keycards to get the max loot from the Monuments. The Red Puzzles are located at Military Tunnels and Launch Site.
These are very hard because of all the forces at each of them waiting to kill you, not counting the excessive amount of Radiation where you need protection and Rad Pills just to complete it. When you go, bring a ton of weapons, Radiation Protection, and Pills, and also 2-3 Fuses. Once you find the Fuse, use everything you got to get to the end. Try bringing friends with you if you are having trouble getting to the loot by yourself.