Even if a thief swaps the SIM card, the IMEI remains the same. This makes it the most reliable "fingerprint" for identifying and tracking a specific piece of hardware across different networks. The Mystery of IMEI Tracker 41
The cult following of "IMEI Tracker 41" likely stems from early 2010s mobile hacking forums (XDA Developers, HackForums). Back then, Android 2.3 (Gingerbread) had security loopholes. A user named "Trax41" or similar released a script that queried unsecured carrier gateways.