Cheap generators simply have a massive, pirated database of VIN-to-Code pairs. If your specific unit isn't in their (often outdated) CSV file, you get nothing. It calculates the code based on the radio’s unique serial number in real-time. This means 99.9% success rates, even for rare, older models like the Alpine CDA-105 or the OEM units in Honda S2000s.
For high-end, aftermarket Alpine units where no database exists, the only "generator" is a physical one. A technician must desolder the EEPROM chip, read the hex data, and locate the code string manually. A Warning on "Brute Forcing" alpine radio code generator better