Once you have confirmed your device is authentic via the serial number check:
Look closely at the exposed metal or plastic body just beneath where the cap sits. The code is laser-etched in tiny text. How to Perform an IQOS Serial Number Check
Researchers have proposed and analyzed broader tracking systems to combat the illicit trade of tobacco products like IQOS: Traceability Systems: A study in Applied Sciences
Open the side door. The 12-digit code is printed clearly on the inside wall of the door hinge mechanism. IQOS 2.4 Plus