If you lose one of your AirPods, Apple is happy to replace it for $69. And if you lose your charging case, Apple will replace it (again for $69), but only if you can provide your serial number, something for which Apple reportedly isn’t always helpful. So it’s a good idea to make sure you can find that serial number, which may be on your receipt from the Apple Store. For online orders, you may have to log in, view the order, and then choose Print Invoice to find the serial number. Or, find the number now — on the AirPods packaging, under the case lid in the indentation for the left AirPod, or in Settings > General > About > AirPods in iOS — and save it in a secure vault like 1Password or even just in an entry in the Notes app.