A Mortality Clock is a magical device that indicates not time, but the health of various people.
Thalia King owns such a clock with herself and her children, Maximilian and Julia King, indicated by its hands. Various positions marked on the clock's face include "Hearty and Hale," "Peaked and Pale," and "On Death's Door." In May of 2009, the clock indicated the death of Maximilian King when his hand passed into the unmarked narrow black wedge. Maximilian's half-sister Alexandra Quick saw the clock shortly after her brother's death prior to his funeral service.