Some early EyeTV USB tuners stored the serial code on a sticker underneath the device. It is rare, but older models like the EyeTV Hybrid (2008) sometimes included a software license key on the hardware packaging.
If you buy a used EyeTV tuner on eBay, ask the seller if they still have the original installation CD case. Many legacy sellers include the serial code as part of the sale.
Unlike today’s subscription-based streaming services, EyeTV 3.6 was a one-time purchase. After installation, the software demanded a to move beyond a 30-day trial. Without this code, the application reverted to a "view-only" mode or stopped launching entirely.