Prerequisite: Have physical access to the laptop in question
1. Windows laptop
- Press Windows key on the keyboard and letter R together to open Run box
- Type CMD in to open Command prompt and click OK
- Type the command wmic bios get serialnumber in Command Prompt and press Enter
- Copy the Serial Number Displayed
2. MacOS
METHOD 1
- Click on Apple menu at the top left of your screen and select 'About this mac'
- The next window will show you the serial number
METHOD 2
You can find it printed on the bottom of the mac