The telecommunications transmission security arrangement comprises first and second transmission paths, each having first and second serially connected circuit means. The first circuit means of said first path is arranged to be connectable to the second circuit means of said second path. The first circuit means of the second path is arranged to be connectable to the second circuit means of the first path, and the second circuit means of each path are arranged to monitor alarm conditions of the transmission paths and set up a transmission path by way of the first circuit means of the first path and the second circuit means of the second path when the first path is determined not suitable for transmission. A transmission path is set up by way of the first circuit means of the second path and the second circuit means of the first path when the second path is determined not suitable for transmission.