No knowledge of the ice detector system on the A320. However at Boeing the 'early' ice detection systems were not terribly reliable and we didn't take credit for them - basically just a hand slapper to remind the crew they were in icing.
The latest generation of ice detectors Boeing calls "PIIDS" - Primary Ice Indication and Detection System". It's a dual redundant system, and when set to "AUTO", PIIDS will turn on engine anti-ice without crew intervention - indication that anti-ice is ON is a EAI (or NAI) display above that engine's indications on EICAS. The crew can still over-ride PIDDS by selecting EAI to "ON" or "OFF". Note that PIIDS can't detect Ice Crystal Icing (ICI) nor does it work on the ground - the crew still needs to select anti-ice manually when on the ground.