Ice detector
mm43;
The ice detector that I'm familiar with (Rosemount, IIRC) detects the formation of ice due to freezing of super-cooled liquid water on its unheated ice-collecting element (*). It does not detect ice crystals floating in the atmosphere. Ice crystals do not adhere to unheated surfaces, but may be 'caught' inside a pitot tube.
(*) Quote from AIAA paper 2006-206 "The Ice Particle Threat to Engines in Flight" by Jeanne G. Mason et al.: In 2002 one large transport aircraft engine powerloss event occurred on an aircraft equipped with dual Rosemount Ice Detectors (RIDs), one on each wing. When exposed to supercooled LWC, ice accretes on the exposed rod of the RID until it reaches a threshold mass, at which point deicing heat is applied to the rod and a ‘trip’ is registered.