A duergar screamer is a construct that uses sonic energy to grind rock into dust. Duergar accused of some crime are trapped within one of these devices, their beards shorn and their ongoing agony channeled into psionic energy that powers the screamer.
The Eternal Order encountered a number of these when assaulting a Duergar Fortress near Frostgorge Sound (see Game-Summaries:11/17 Recollections)
They are dangerous, but fragile. Breaking the construct causes horrific death for the dwarf trapped within.