Visible crew/equipment: During the zero-gravity fight scene in the hotel room, it is possible to see a crew member's hand briefly resting against the end of the bed when Arthur and the projection are fighting on it.
Visible crew/equipment: Right before Cobb and Arthur go to the roof to find Saito having Nash in the Helicopter, Cobb and Arthur are in the Hotel Room with windows in the background. In the reflection of the windows, you can easily see the camera and the microphone.
Chosen answer: The details are never explained in the depth, but all the dreamers are connected via the briefcase, so it seems likely that the briefcase acts in some way as a networking hub for them to share the dreamspace.
Tailkinker ★