The Home button, on the iPhone models with Touch ID, houses the Touch ID sensor, which gives you the option to use your fingerprint to verify authorized access to your iPhone from the Lock and to authorize purchases from the iTunes, App, and iBook Stores. With iOS 8, Apple opened this option to developers so you’ll be seeing it as an option with other apps soon, too.
You may have set up Touch ID when you set up your iPhone. If not, follow these steps to add your fingerprint or that of someone else, like a child or significant other. You can also name or delete fingerprints.
You still have to set up a passcode to use Touch ID, for two reasons: When you turn your iPhone on, you have to enter the passcode, and if for some reason your fingerprint doesn’t work, you can still unlock your iPhone.
Open the Settings app and tap Touch ID &Passcode.
If you previously assigned a Passcode to your iPhone, you have to enter it before you can access the Fingerprint setup. If you haven’t set up a passcode, you can do it at the same time you add a fingerprint.
Tap Add a Fingerprint.
Place your finger, or thumb, on the Home button.
The fingerprint on screen begins to redden as the whorls and swirls of your finger are memorized.
Lift and replace your finger on the Home button and roll it around so the Touch ID sensor can memorize the edges of your finger.
After registering the flat part of your finger, iPhone prompts you to adjust your grip. Tap Continue and place the tip and edges of your finger on the Touch ID sensor.
When your fingerprint is successfully read, tap Continue.
If you haven’t set up a passcode, tap a four-digit passcode on the keypad that appears (or type a complex passcode on the keyboard if you turned Simple Passcode off), otherwise go to Step 8.
Re-enter the passcode on the subsequent screen.
Choose when you want to use your fingerprint to authorize actions by tapping on iPhone Unlock (to use Touch ID to unlock your iPhone) and/or iTunes & App Store (to authorize purchases with Touch ID).
(Optional) To change the name or delete a fingerprint, do one of the following:
Name the fingerprint: Tap the fingerprint and then type a name, such as “Barbara’s Index” or “Lucy’s Paw.”
Delete the fingerprint: Tap the fingerprint in the list, and then tap Delete Fingerprint.
Even when a passcode or fingerprint is required to open the Lock screen, you, or more likely someone who wants to use your iPhone because you’re incapacitated, can make an emergency call by tapping the Emergency button in the bottom-left corner of the passcode screen. After tapping the Emergency button, a Medical ID button appears that lets the Good Samaritan who’s helping you contact your next of kin.