TL;DR
Rust keycards are a progression chain, not random loot. Green starts the puzzle loop, blue moves you into better monuments, and red opens the highest-value puzzle rooms. In most cases, you also need an electric fuse, so the card alone is not enough.
Looking to create your own gaming server?
Rust Server Hosting
If you want the simple route, it usually looks like this: get a green card from an easy monument, turn that into a blue card through a low-tier puzzle, then use the blue card at a higher-tier monument to get a red card. Once you have red, the best monument rooms open up.
How Rust keycards actually work

There are three access levels in Rust: green, blue, and red. Each one opens a different tier of puzzle door, and the loot usually improves as you move up the chain.
That is why experienced players do not think of keycards as separate items. They think of them as a route. A green card is useful because it becomes a blue card. A blue card matters because it becomes a red card or gets you into stronger monument rooms. A red card is the point where monument puzzles start paying out properly.
The other thing people forget is power. A lot of puzzle rooms need an electric fuse in the fuse box before the card reader works. If you reach the room without one, the run is wasted.
Rust Green keycard locations

Green keycards are the easiest ones to get and the least painful to farm. The most common early spots are Lighthouse, Oxum’s Gas Station, Abandoned Supermarket, and Junkyard. Depending on the map and monument set, players also commonly check places like Abandoned Cabins or Ferry Terminal.
This is why green cards are the “start here” card. You can usually grab one without committing to a heavy radiation route or a long monument setup.
Green cards are then used in lower-tier puzzle rooms at places like Harbor, Satellite Dish, Sewer Branch, and some green-door monument paths.
Rust Blue keycard locations

Blue keycards usually come from completing green-card monument puzzles. The classic sources are Harbor, Satellite Dish, and Sewer Branch. If you do not want to run that step manually, Outpost is often the cleaner option, because you can buy a blue keycard there for scrap.
That makes blue the flexible card. You can earn it through monument progression or skip part of the chain and buy it if your wipe path makes that more efficient.
Once you have one, blue keycards open a better tier of monument rooms, including places like Airfield, Train Yard, Power Plant, Water Treatment, Arctic Research Base, Underwater Labs, and similar higher-value puzzle routes.
Rust Red keycard locations

Red keycards come from blue-card monuments. The standard places people think of first are Airfield, Train Yard, Power Plant, and Water Treatment.
This is where monument runs stop feeling casual. These locations are busier, more dangerous, and more likely to punish sloppy routing or weak gear. Still, this is the step that matters most, because red cards are the gateway to the best puzzle rooms in Rust.
Red keycards are typically used at Launch Site, Military Tunnels, the Oil Rigs, and higher-end locked areas that are actually worth fighting over.
The fastest keycard route
If your goal is efficiency, the best route is usually simple.
Start with a green card from a low-risk monument. Use that green card to complete a lower-tier puzzle and get a blue card, unless buying one at Outpost saves time. Then take the blue card into a stronger monument and turn it into a red card. After that, stop thinking about cards and start thinking about which red-card monument gives your group the best return right now.
That is the part newer players often miss. The card itself is not the reward. The room behind it is.
What players get wrong
The first mistake is treating keycards like they work by themselves. Many doors need power, which means you need the right fuse and the right route through the monument.
The second mistake is farming the wrong tier for too long. If you already have the gear and scrap to move up, do it. Sitting on a green-card loop when your wipe is ready for blue or red is just slow progression.
The third mistake is carrying a red card with no plan. Red cards matter most when you already know which monument you are going to run, what resistance or gear you need, and how you are getting out.
Conclusion
The easiest way to understand Rust keycards is to stop seeing them as separate items and start seeing them as a ladder. Green gets you moving. Blue opens the midgame monuments that actually feel worth contesting. Red is where the best puzzle rooms begin.
If your monument runs feel messy, the fix usually is not more gun skill. It is better routing. Bring the fuse, bring the right card, and know which room you are heading for before you step inside.