Limitation collar

A limitation collar was a form of restraint placed on visitors to the Leisure Hive on Argolis who were accused of criminal activity.

History
The collars were programmed to allow the wearer to roam freely around the Leisure Hive, but forbade them access to certain areas. If the wearer entered a forbidden area, the collar would tighten around their neck, strangling them, and would also contract if the wearer attempted to remove it.

The Fourth Doctor and Romana II had limitation collars placed on them by Argolin tour guide Vargos by order of Mena, after the Doctor was accused of murdering Stimson. The Leisure Hive areas to which they were forbidden access while wearing their limitation collars were the Great Recreation Hall where the TARDIS stood, the laboratories, the Board Room, and the Shuttle Station. (PROSE: Doctor Who and the Leisure Hive)

The Doctor and Romana were freed by Hardin using a key he had borrowed from the Leisure Hive's Security Office. (TV: The Leisure Hive)