From D&D Wiki
This magical item manifests initially as a plain, silver metal earbud piece. Once someone puts it on, the metal reacts to the contact and warps to infiltrate the appropriate orifice, usually resulting in half-deafness. The piece then forms a metal rod or likewise extension on the side where it was placed, but is of negligible weight (>1 lb.). This magical accessory gives the wearer truesight for 30 feet, as well as the ability to cast all cantrips and 1st level spells. This object cannot be taken off once used without taking 2D8 magical slashing damage, and can only be used by humanoid creatures with the ability to hear.