Ghost Radar

The is an object mentioned in.

Location and Uses
The Ghost Radar is a device used by Pamela's Father in his studies of the supernatural in Ikana Canyon. He only ever mentions the Radar going off if Link wears any of his Transformation Masks in his presence. The Radar's response is different than usual when detecting Link, however, reading him as both similar to a ghost and different from one at the same time. This response leads Pamela's Father to ask Link if he can study him.

The strange response that occurs as a result of Link's presence in his Deku, Goron, or Zora forms is undoubtedly a result of him being alive, and yet wearing a mask containing a spirit at the same time.