Locus (The Abominable Snowmen)

A locas was a small model yeti that could be programmed as a homing device by producing a signal similar to a control sphere. As a result, it would summon a real yeti. (DW: The Web of Fear)

They could also be controlled by moving them on a chess board. This would also send a yeti to a certain area. (DW: The Abominable Snowmen)