ID Code Box (Camry HV) / Transponder Key ECU (Prius) / Immobiliser ECU
Think of the ID Code Box as “lock box” holding keys. Just as a traditional key is cut with a specific pattern of peaks and valleys to match a specific pattern of wafer placement in a lock cylinder, the bits of the electronic keys held in the ID Code Box must exactly match the pattern of the bits of the electronic keys held in other ECUs on the same car.