A lesser-known but theoretically life-saving feature of Apple's iOS Health app is Medical ID -- a quick guide for nurses, doctors, ambulance crews and others in an emergency. Here's how to set it up on an iPhone running iOS 10.
Within the Health app, tap on the Medical ID tab in the bottom right. On an iPhone 6s or 7, 3D Touch can be used to jump straight to the tab from the app's homescreen icon.
The first thing visible is the heart of Medical ID -- a card of vital information and contacts. To actually add anything to it, you'll have to find and tap the Edit button, which may be further down the page if some fields are already populated.
Once opened, the Edit option displays a particularly important toggle up top: "Show When Locked." Unless you keep your iPhone permanently unlocked, without a passcode or Touch ID, this setting should always be switched on. In case of an emergency, medical crews can check your card by tapping "Emergency" from the lockscreen's passcode menu, and then hitting "Medical ID."
As far as data goes, basics include making sure your name, photo, and date of birth are in order, as well as height, weight, and blood type. Note that even with a smartscale, weight isn't automatically updated.
You can also specify whether you're an organ donor. In the U.S., in fact, the bottom of the main Medical ID screen -- before hitting Edit -- includes an option to register with Donate Life America.
Back on the Edit page, the next important step is to add emergency contacts medics can call. These are limited to people from the iOS Contacts app, but you can additionally specify their relationship, such as "spouse" or "friend."
By this point, you've probably noticed several other data fields: Medical Conditions, Medical Notes, Allergies & Reactions, and Medications. These are simple text fields, so you'll have to manually enter any information. A good use for Medical Notes is specifying who to contact first, so that your spouse for instance is notified before your parents in another country.
That's about it for Medical ID, but there are a couple of points to make about privacy. Note that while no one can edit your card from the lock screen, you may want to be careful about what you add to it -- even a curious friend or coworker could learn deep personal secrets. If you change your mind about Medical ID, the Edit screen includes a "Delete Medical ID" option at the very bottom.
For tips on using the Health app in general, be sure to check out our recent starter guide.