Trilanic activator

A trilanic activator was a device created and used by the Zygons to control their Skarasens. When activated, it sent out a signal and called the Skarasen to wherever the control was. Like most Zygon technology, the trilanic activator was biological in design. It was hand-sized and had a texture like wet skin. It would activate and could be regenerated when in an area of high diastellic transmissions.

A group of Zygons used a trilanic activator in 1909 to control their two Skarasens. The Tenth Doctor later stole it and planned to use it to put the Skarasens to sleep. It was regained by the Zygons after the Doctor's capture. (PROSE: Sting of the Zygons)

A trilanic activator was used by Zygons in the 1970s. Madra was sent to retrieve it from the Fourth Doctor, using the body-print of Harry Sullivan to avoid detection. However, Sarah Jane Smith noticed his altered behaviour and pursued him, a chase that led to his fall from the rafters of a barn and his impaling. The Fourth Doctor used the activator to lead the Skarasen away from UNIT's temporary base. It bonded to his hand, preventing him from casting it away and he was almost killed by the creature, but Harry used the controls in the Zygon ship to detach it. The Skarasen destroyed the activator, prompting it to return to Loch Ness. (TV: Terror of the Zygons)