Check the sticker on the bottom of the laptop
Check the label under the battery if the battery is removable
Open the BIOS or UEFI setup and look for the serial number
On Windows, open Command Prompt and run `wmic bios get serialnumber`
On Windows PowerShell, run `Get-CimInstance Win32_BIOS | Select-Object SerialNumber`
On macOS, click the Apple menu, select About This Mac, and note the serial number
On Linux, run `sudo dmidecode -s system-serial-number`
Check the original box or purchase receipt
Check the manufacturer’s support app or account portal
Contact the laptop manufacturer with the device details if the serial number is missing