Your lot number is needed to process a warranty claim. Here's where to look depending on your product type:
Headphones & Headsets
Check the inside of the headband — the lot number is printed or molded into the plastic on either the left or right side. You may need to flex the headband slightly to read it clearly.
If you still have the original packaging, the lot number is also printed on the poly bag.
Ear Buds
The lot number is printed on the poly bag your ear buds came in.
Here are some example photos of the lot number on various different products.
