Have you decided to help Chorban scan all the Citadel Keepers but can't find all 20? Here are all of their locations.
InstCitadel Keepers can be found all over Presidium, Wards, C-Sec and one at the Docks in Mass Effect. Here is a list of all 20 keepers, sorted by their locations for easier completion. All the locations on the map are marked by the cursor that looks like a big circle.
One keeper can be found next to Chorban, you can scan it as soon as the Salarian gives you the assignment.
As soon as you scan it, turn to the right and go past Rear Admiral Kahoku to find the second keeper.
The third, and final keeper can be found on the opposite side of the Tower. Start going towards the elevator from the position where you scanned the second keeper and turn left before you go down the stairs, it should be easy to spot from there. After the third scan, go and take the elevator to the Presidium.
The first keeper is straight ahead of you as you exit the elevator from the Council Tower, doing its thing next to Avina.
After that, you can either walk to the Emporium in the Financial District or take Citadel Rapid Transit to the location. Go behind the Hanar vendor into the back room where you will find one keeper.
When you scan it, leave the Emporium and turn to the right. Hug the right wall and you will run into the next keeper.
Instead of taking the stairs, backtrack a little and go beneath the overpass. Proceed straight ahead until you reach Consort's Chambers. One keeper will be just outside the entrance.
Head for the embassies and go to the Volus and Elkor office to find another keeper.
Now turn back and go toward the embassies lounge, which will be dead ahead when you go through the embassies door. However, take the right turn instead of left and go through the only available door to find the next keeper at the end of the room.
Now go to the embassy lounge and take the door that leads you to the balcony, behind the bar. You will find another keeper there.
After that, leave the embassies and go towards the Citadel Tower until you see the door to Flux and Wards Access on the right. Go there to find the last keeper on the Presidium. Then take the stairs down to the elevator, use it and you will reach Flux and Wards Access.
Flux and Wards Access is your first stop. Go down the hallway and enter the last room on the left. Scan the keeper and then proceed to the elevator just behind you to enter Wards properly.
As you leave the elevator, take the first door to the right to access the Alleyway. Scan the keeper in front of you and proceed in the same direction until you reach the Citadel Rapid Transit node next to Chora's Den approach.
Take the door to the Markets and use their stairs to reach Upper Markets. As you leave the stairs, the keeper will be on your left, behind Expat the Volus vendor.
Now leave the markets on the same floor and you will immediately spot a left turn that leads you to Flux. Go there and then take the stairs that lead you to the casino with all the Quasar machines to find another keeper there.
Leave Flux and go left as you descend the stairs, past the Med Clinic where you found Garrus previously. You will find the keeper in a small room there.
Now backtrack a bit, to the set of double stairs you passed on your way to the clinic. Take the stairs down and you will see a keeper next to Officer Lang. Scan it and take the elevator to C-Sec Academy.
As you leave the elevator, hug the right wall until you reach the C-Sec Requisitions Office. Scan the keeper in the room and then go to the opposite side of the academy.
Traffic Control is on the western side of the C-Sec Academy. You will need to visit the westernmost room on the map and the keeper will be to your right. Scan it and go back to the middle of the academy, to the elevator that leads you to Docks.
There is only one keeper here. As you leave the elevator, just go straight ahead and you can't miss it. Alternatively, the keeper will be to your left if you are entering Docks by leaving Normandy.