Comfork

The Comfork is an item featured in the A Link to the Past comic. It is a crystal tuning fork that, when vibrating, allows people to communicate with other beings that are in different worlds.

History
After Link frees the Maiden from the Palace of Darkness, she thanks the young hero and grants him the Comfork. Later, the Comfork begins to ring and Link sees an image of Sahasrahla and the rest of his friends back in Kakariko. Although at first Sahasrahla disregards Link's voice as having been his imagination, Sahasrahla and the others eventually communicate with Link  and discover that the Comfork allows them to speak with each other even  though they are on different planes of existence.

Later, when Link and Epheremelda realize that the Swamp Palace is completely dried up, the young hero uses the Comfork to call Sahasrahla for help and ask him to investigate the area in the Light World. Using the device permits Link to eventually enter the inner portion of the palace and free another maiden.