Summoning device

The Summoning device was Silurian technology which was capable of calling forth other Silurians, thus serving as a communication device.

The machine was a hand-sized device which, when activated, emitted a burst of resonating sonic bursts that a Silurian and certain animals like dogs could hear. It was also capable of opening doorways within Silurian bases.

The Silurians gave a summoning device to one of their agents in order to recover a wounded and lost member of their race that was being hunted by humans on the surface. The Third Doctor took the device from the dead Dr Quinn and used it to enter the Silurian base in the caves. (DW: Doctor Who and the Silurians)