To find out who's calling, normally you'd have to take out your iPhone or look at your Apple Watch, but you can actually have your AirPods (or any connected headphones) announce who it is, saving you the trouble.
To enable this feature, simply follow these steps.
- On your iPhone, launch the Settings app.
- Tap Phone in the list.
- Tap Announce Calls under the Calls heading.
- Tap Headphones Only so that a tick appears alongside the option.