Like all Apple products, your AirPods have a unique serial number.
Here's how to find it!
When you first purchase an Apple product, you're encouraged to register it with your Apple ID; this not only lets you locate your device in Find My iPhone, but also makes it easier to service or replace a broken or missing device.
Even if you've registered your AirPods with your Apple ID, however, it's still a good idea to have its serial number located and written down: You'll need it if you ever need to replace a set of broken or lost AirPods. Here's how to find this number!
Every AirPods case has a unique serial number: You can find it on the inside of the lid, above the left earbud. It's (no surprise) set in incredibly small type, and you might want to use your iPhone's camera to properly capture (and zoom in on) the serial number.
If you can't read the serial number on the inside of your AirPods case, you can also grab it from the Settings app on your iPhone or iPad. Here's how.
Tap on AirPods at the bottom of the screen. (If you don't see this field, double-check that your AirPods are connected via Bluetooth.)