The Psychic Spyglass (霊透眼鏡 [れいとう ･ レンズ], Reitō Megane [Reitō Renzu]; lit. "Spirit Filtering Spectacles") is a tool of Yusuke's Spirit Detective Kit. It is the first item to make an appearance in the anime.
This psychic spy device, appearing as something akin to a monacle, features a lens with a green frame, accented by a blue tassel which doesn't appear to serve any purpose.
Allows the user to peer through all manner of materials including clothing and walls, rendering them transparent within the lenses field of view and revealing what lies beyond. Given its special properties, it is highly likely this spirit item allows the user to see objects and color in the dark.
Spirit Detective Saga
Yusuke is given the Psychic Spyglass on the roof of Sarayashiki Jr. High. Upon receiving it his initial instinct is to test it out by trying to see through Botan's clothes. She prevents this from happening by taking an oar upside Yusuke's head. Later, when his teacher, Iwamoto, accuses him of thieving items belonging to various students, he uses the item, with a prompt from Koenma, to identify the missing items in Iwamoto's pocket, freeing himself of blame in the process.