A Melder is a silver weapon. It has a sleek, curved handle connected to a triangle of silver with a single button located in the center. When fired from a distance, this weapon only stuns the afflicted person; at close range, and depending on where the person was shot, it can cause permanent physical damage, mental damage, or both.
Members of the Neverseen repeatedly threaten Sophie and her friends with Melders. These weapons were first mentioned in Book 1: Keeper of the Lost Cities, where the Neverseen threatened to shoot Dex during the kidnapping scene. They were later mentioned in Exile, where Keefe and Fitz use one and in Everblaze, where Sophie and Gethen are shot by them. Gisela also used one to threaten Biana in Book 3.
Alden taught Biana how to pull someone out of the daze that a Melder causes. When Sophie was shot, she used the method to help Sophie. The method consists of placing two fingers under the afflicted individual's temples and pressing hard. It is described to be highly painful.