Some devices use a single built-in administrator account created at factory that must be set at first login or otherwise remains with a default password until changed.
Certain models ship with a device-specific serial-number–derived password or an activation code printed on a sticker. In these cases the “default” is unique per-unit.
Firmware updates and different product lines (e.g., standalone access controllers, time-attendance terminals, door controllers, or Web3.0 management interfaces) may change or remove legacy defaults.
Web interface behavior:
Historically, the default credentials for ZKTeco devices (including older Web 3.0 implementations) are widely known and documented in public manuals.