A one-way pass-through system with return block for use in buildings having the following features: - an entrance door arrangement and an exit door arrangement offset therefrom are provided; - first and second side wall arrangements (3a, 3b) are provided between the entrance door arrangement and the exit door arrangement defining a pass-through area between the entrance door arrangement and the exit door arrangement; - a sensor device is provided comprising several sensors (5a, 5b, 5c) and configured to detect persons: a) in front of the entrance door arrangement; b) in the pass-through area and behind the exit door arrangement; - a control device is provided configured to receive and evaluate sensor data of the sensor device and to enter different operating modes, with the entrance door arrangement and the exit door arrangement being controlled respectively by the control device according to the operating mode, characterised in that - in addition to a normal operating mode or a lock operating mode, the control device is configured to enter a safety operating mode and to close the entrance door arrangement, a) if the evaluation of the sensor data reveals that a person is walking back towards the entrance door arrangement in the pass-through area; and b) if the evaluation of the sensor data reveals that a person is walking back towards the pass-through area behind the exit door arrangement; - an illumination means is provided, which is arranged in the pass-through area and configured to illuminate the pass-through area in different colours; - the control device is also configured to control the illumination means such that it illuminates the pass-through area a) with light in a red colour, if the control device is in or enters the safety operating mode, and b) with light in a green colour, if the control device is in or enters the normal or lock operating mode. - an entrance door arrangement and an exit door arrangement offset therefrom are provided; - first and second side wall arrangements (3a, 3b) are provided between the entrance door arrangement and the exit door arrangement defining a pass-through area between the entrance door arrangement and the exit door arrangement; - a sensor device is provided comprising several sensors (5a, 5b, 5c) and configured to detect persons: a) in front of the entrance door arrangement; b) in the pass-through area and behind the exit door arrangement; a) in front of the entrance door arrangement; b) in the pass-through area and behind the exit door arrangement; - a control device is provided configured to receive and evaluate sensor data of the sensor device and to enter different operating modes, with the entrance door arrangement and the exit door arrangement being controlled respectively by the control device according to the operating mode, - in addition to a normal operating mode or a lock operating mode, the control device is configured to enter a safety operating mode and to close the entrance door arrangement, a) if the evaluation of the sensor data reveals that a person is walking back towards the entrance door arrangement in the pass-through area; and b) if the evaluation of the sensor data reveals that a person is walking back towards the pass-through area behind the exit door arrangement; a) if the evaluation of the sensor data reveals that a person is walking back towards the entrance door arrangement in the pass-through area; and b) if the evaluation of the sensor data reveals that a person is walking back towards the pass-through area behind the exit door arrangement; - an illumination means is provided, which is arranged in the pass-through area and configured to illuminate the pass-through area in different colours; - the control device is also configured to control the illumination means such that it illuminates the pass-through area a) with light in a red colour, if the control device is in or enters the safety operating mode, and b) with light in a green colour, if the control device is in or enters the normal or lock operating mode. a) with light in a red colour, if the control device is in or enters the safety operating mode, and b) with light in a green colour, if the control device is in or enters the normal or lock operating mode.