A classic hallmark of a counterfeit unit is a serial number consisting of the same repeating digit (e.g., 1111111, 1234567, or 0000000). Real Sony serial numbers are randomized sequences. If you open the ear cup and see 1234567, you are holding a fake.
Look inside the left ear cup.
The serial number on your Sony XM4 is more than just a string of digits—it is the key to warranty service, authenticity verification, and software support. Whether you own the plush WH-1000XM4 headphones or the compact WF-1000XM4 earbuds, take 30 seconds right now to do three things: serial number sony xm4