CuboAi's serial number starts with "CQ" (Cubo Ai) or "CB" (CuboAi Plus) and can be found on the bottom of the camera. You'll need to remove CuboAi/CuboAi Plus from the stand to see the serial number. Alternatively, the serial number can also be found on the box sleeve.
Sleep Sensor Pad
The serial number is located on the bottom of the Sleep Sensor Pad underneath the barcode, and starts with "CM".