Blood compass

A small device that is used to detect magical sources in the near vicinity.
The most basic forms are used by adding a drop of blood to a receptial. The trace levels of Uhd within the blood stream are used to power the contraption and swing the copass needle to the closest and strongest source of magic within 50 or so metres (stronger sources can be detected from further afield.
This can point to stone magic devices, sources of crystaline Uhd, or even practitioners of magic who are performing blood magic transformations of any sort.