The security system in Antarctopolis was provided by red robots who were able to change their facial expression at will. After the Sixth Doctor exited the penguin preserve without going in, along with Peri Brown and Frobisher, the robots pursued them to the amusement park, where the Doctor was captured, but Peri and Frobisher avoided capture on the carousel.
A red robot brought the Doctor into his cell in the Antarctopolis asylum. Unknowingly, another robot gave out the Time Lord's location to Peri and Frobisher, who had now disguised as a young child.
After infiltrating the asylum, Frobisher and Peri passed a robot in the hallways. Frobisher, who was now in disguise as a hospital attendant, passed the robot with no problem. (COMIC: Façades)