The UFO Key in Sell Lemons is one of the best-kept secrets in the entire game. Hidden deep inside the sewer maze, it requires solving a multi-step lever puzzle before you can even reach it. The payoff is real though: a permanent +2% cash bonus per investor and the Good Samaritan badge. This guide walks you through every lever, every turn, and the exact path to the alien who accepts the key. If you play Roblox idle games, this is worth the effort.
What do you need before going after the UFO Key?
Before entering the sewer with any intention of grabbing the UFO Key, you need to have completed at least one Rebirth. Rebirth unlocks after you reach the sextillion income range and build the Lemon Trading income building. Once you Rebirth, Joe the Alien appears in your yard. Talk to him at least once to activate your investors. The UFO Key route only becomes accessible after you have an active investor.
Drop into the sewer here
With an investor active and a fresh lever state, head to any sewer manhole and drop in.
The full lever sequence
The sewer has four colored levers: Blue, Red, Green, and Purple. You will hit them in a specific order, and some levers get toggled multiple times. Here is the complete sequence before the step-by-step breakdown:
Use the respawn button after each lever to return to the sewer entrance fast. Walking back through the maze every time is a waste of time.
How to activate the Blue Lever
From the central leaderboard area, face the Most Cash board. The green text on the wall will be on your left. Head in the opposite direction, toward the green text side, and enter that hallway.
At the first intersection, take the second right. Continue forward past another right-side turn until you spot a green line on the floor to your left. Do not follow the green line. Instead, keep going straight and take the hallway to the right of it.
When the corridor splits again, take the left path past the red line, then follow the purple-lined route all the way to the end. The Blue Lever sits at the terminus. Interact with it, then respawn.
Blue lever at maze end
How to activate the Red Lever
The Red Lever is the most straightforward of the four. From the leaderboard area, face the Most Fruits Picked board. Head straight down that hallway. You will pass a locked gate on your right. Continue past it and enter the maze opening on the left.
The path is nearly linear. Side routes dead-end quickly, so just keep moving forward and you will reach the Red Lever without any real navigation challenge. Pull it and respawn.
How to activate the Green Lever
The Green Lever maze entrance sits to the right of the Most Cash leaderboard. Head down the hallway and take the first left, then a right at the next turn. Continue forward past both the red and blue floor lines.
Stay on the left-side paths as the maze branches. Eventually you reach a corridor with three options: right, left, and a farther-left path. Take the first right here and the Green Lever is right there. Pull it and respawn.
How to activate the Purple Lever
The Purple Lever entrance is on the same side as the Blue Lever hallway. Walk toward the green text on the wall and enter that side, but this time hug the left of the corridor rather than the right.
Take the left, then a right. Continue through the maze until you spot a red line on the right side of the floor. Keep going until a second red line appears. Ignore that path and take the left turn instead. Follow the route until you cross a green line, and the Purple Lever is just beyond it. Pull it, then respawn and head straight back to reactivate the Red Lever.
How to find the UFO Key location
After deactivating both the Green and Red Levers in steps 7 and 8, the path to the UFO Key opens up inside the Blue Lever maze.
Enter the Blue Lever hallway the same way you did in step one. Follow the route until you reach the area with the first green line on the floor. This time, instead of going straight, take the left turn. Cross the green line and keep walking until a blue line appears. Cross it, then cross the purple line that follows.
At the end of that path, the UFO Key unlocks for your character. Pick it up. You are not done yet though. You still need to deliver it to the alien.
How to deliver the UFO Key to the alien
After grabbing the key, return to the sewer center and pull the Red Lever down (fifth interaction), then head to the Green Lever and pull it down as well (third interaction).
With both levers in the correct position, start the Green Lever path one more time. After taking the first left, take another left, and then a second left immediately after. A door that was previously closed will now be open. Inside, behind bars, you will find the hidden Alien.
Interact with the alien and hand over the UFO Key. The reward is permanent: your investor returns increase by +2% cash per investor, stacking with every investor you own. You also earn the Good Samaritan badge.
Is the UFO Key worth the effort?
Honestly, yes. The +2% per investor scales directly with how many investors you have active, so the more you have built up post-Rebirth, the more this bonus compounds over time. The puzzle itself takes 20 to 30 minutes on a first run, mostly because the maze navigation is genuinely confusing without a reference. The Good Samaritan badge is a nice bonus for completionists.
For more Roblox guides covering similar hidden progression systems, check out the Sailor Piece Boss Keys guide for a look at another key-hunting mechanic that rewards patience, or the Spirit Keys farming guide if you want to see how Sailor Piece handles its own boss unlock system.