Locus (The Abominable Snowmen)

A locas is a small model yeti that can be programmed as a homing device by produsing a signal similar to a control sphere and as a result would summon a real yeti. [DW The Web of Fear]

They can also be controlled by moving them on a chess board and would also guide a yeti to a certain area. [DW The Abominable Snowman]