Where can I find the serial headphones
iPhone 6s, iOS 14
AFAIK, the Apple EarPods do not have serial numbers. If your goal is to have them replaced, they are covered by Apple's one year limited warranty against manufacturing defects. However, normal "wear and tear" is not covered and replacements would be at your cost.
It would be helpful if you could be more specific as to the brand and type.
If you have the original packaging, you may find the serial number next to the barcode. You can also find the serial number on the original product receipt or invoice if they actually have one.
Otherwise ask APple:
Contact Apple for support and service --> "See a list of Apple phone numbers around the world."
Click here --> https://support.apple.com/HT201232
How to find serial number on your normal headphones
