Q: How do I find out the warranty on my in ear headphones

Same as the warranty on your phone. Plug the SN of your phone in here:

https://selfsolve.apple.com/agreementWarrantyDynamic.do

See if you have any warranty left.

All our iPhone boxes have the serial number on base of box a 3G ,4, 5 and 5s all have exactly the same label with sn number in each case

You use the SN of your phone...Settings>General>About...that's what you plug in the link I provided you. Your headphones have the same warranty as your phone, everything you got in the box does.

There is no SN for your headphones.

Copied from my initial post:

Plug the SN of your phone in here:

Then it look at the box the headphones came in.

Then they came with a one-year warranty...you'll need your receipt, or if you go back to the store where you purchased, they should have a record of the purchase.

Contact the manufacturer of your headphones.  If Apple, they have a 1 year warranty.  Take them in and let Apple look at them.

Copied from my last post:

"if you go back to the store where you purchased, they should have a record of the purchase."

Good luck.