Medical ID allows you to enter important medical information into your iPhone that first responders can access without needing your device's passcode from the lock screen (by tapping on Emergency and then Medical ID on the next screen).
It's easy to fill in this Medical ID information - if you know where to go! Launch the Health app then tap on Medical ID at the bottom-right of the screen, and then choose Create Medical ID.
There you can list your name (along with a photo), date of birth, list of medical conditions, blood type, organ donor status, notes, allergies, reactions, weight, height, and medications. You can also list details of your emergency contact.
Importantly, you can also configure whether this information is accessible when the iPhone is locked.
You are free to edit or delete this information at any time.