Abstract: A security transfer unit includes a hollow box-structure that has open ends on opposite sides of a security barrier and is supported from side-frames with a clearance underneath. A rolling shutter encircles the box-structure to block access to either end to the chamber through openings in the unit casing. The shutter is driven to bring an aperture therein into register with the openings in turn so that access to the chamber can be gained through only one of them at a time. Drive is in one direction only and is interrupted with the shutter blocking both openings when the aperture is located in register with an aperture in the box-structure, so as to enable viewing of the contents of the transfer chamber through a window above.