The killing device was invented in the early second half of the fifth century of the Human Era by Blayce the Gallan. These devices were a crucial benefit for the Scanran side at the beginning of the Scanran War. In Mid-August of 460 HE, Keladry of Mindelan faced her first killing device, which she described as a metal beast. They are described as being insect- or ratlike.
The devices ran on the souls of dead children. The only way to 'kill' a device was to puncture the head, at which point the spirit of the child, seen as white vapor, was released and could be heard for a few moments. They were made of metal, including metal-coated giants' bones. They had knife fingers and toes, sharp teeth, and a tail with a metal spike on it, and were about seven feet tall. They were also extremely strong.
The quality of the device seems to have been influenced by the state of the child whose spirit ran it. Kel observed one device that was slower and clumsier than the others, and hypothesized that the child killed to run it may have been mentally unsound.