Travel dial

A travel dial was a wrist-worn teleportation device used for travel on the planet Marinus. Considering that the First Doctor was familiar with it but not with the planet, it must have been used on other planets, as well. The wearer merely had to twist the dial in order to effect instantaneous travel to the pre-programmed destination.

Arbitan gave one each to the First Doctor, Susan, Ian Chesterton and Barbara Wright in order to make it easier for them to find the keys to the Conscience of Marinus. (TV: The Keys of Marinus)