Check the sticker on the bottom or back of the computer
Check the original box or purchase receipt
On Windows, open Command Prompt and run `wmic bios get serialnumber`
On Windows, open PowerShell and run `Get-CimInstance Win32_BIOS | Select-Object SerialNumber`
On Mac, click the Apple menu, choose About This Mac, and note the serial number
On Linux, run `sudo dmidecode -s system-serial-number`
In BIOS or UEFI, look for System Information or Product Information
Check the manufacturer’s support app or system utility
Check the device label inside the battery compartment if applicable