iPhone Duo Unlocks Without Touch ID via Apple Watch on Series 9 and Newer

Q: Why does the foldable iPhone Duo rely on a smartwatch for a smooth unlock instead of the Face ID technology users already expect?

The iPhone Duo relies on an Apple Watch for smoother unlocking because the foldable design appears to have pushed Apple away from Face ID hardware, leaving side-button Touch ID as the built-in biometric system. Reports and Apple’s own setup guidance indicate the Duo does not include the familiar Face ID sensor array found on standard iPhones. In a foldable phone, that hardware is harder to integrate cleanly: the device has two displays, an under-display inner camera, and a compact outer screen, and duplicating or adapting Face ID for both open and closed use would add space, cost, and engineering complexity. A fingerprint sensor in the side button works in either posture because it stays in the same place whether the phone is folded or unfolded. That creates a usability gap for users accustomed to hands-free Face ID. Apple’s answer is “Unlock with Apple Watch,” which lets a nearby, unlocked watch authenticate the phone without a fingerprint scan. In practice, it serves as the closest substitute to the seamless feel Face ID normally provides on other iPhones. Apple is also careful about the limits of that feature. Watch-based unlock is mainly for opening the phone itself; it does not replace stronger identity checks for Apple Pay, passwords, or protected apps. So the Duo’s setup suggests Apple chose a simpler, more consistent hardware authentication method for a complicated new form factor, then used the watch to restore some of the convenience users expect.

Q: Could Apple's seamless watch-unlock feature for the iPhone Duo accidentally give someone else access to your device while you are standing nearby?

Yes, that risk appears to exist in a limited, real-world way. Apple’s watch-unlock feature for iPhone Duo is designed to work when the paired Apple Watch is on your wrist, already unlocked, and close to the phone. That means the system is relying largely on proximity and the trusted watch state, not on a fresh fingerprint scan each time. If someone else physically picks up or snatches the iPhone Duo while you are standing nearby, the phone could unlock before you react. Apple’s broader documentation for Unlock with Apple Watch on other iPhones helps explain the safeguard: when the watch unlocks the phone, the watch gives haptic feedback and shows a notification with a “Lock iPhone” option. If the unlock was unintended, you can immediately relock the phone from the watch, and the next unlock then requires the iPhone passcode. That reduces the danger, but it does not eliminate the brief window in which the device may already be open. There are also important limits to what the feature does. Apple says watch-unlock is mainly for getting past the lock screen. It does not replace stronger authentication for Apple Pay, saved passwords, or password-protected apps, which still fall back to the phone’s normal security checks. So the feature is convenient, but not risk-free. If you are worried about opportunistic access in crowded places, using Touch ID instead of watch-unlock would be the more cautious choice.

3 articles · Updated · MacRumors · Oct 24

Apple lets iPhone Duo owners unlock the phone with a paired Apple Watch, avoiding the side-button Touch ID sensor entirely once the feature is enabled.
Settings on iPhone Duo now include “Unlock with Nearby Devices,” where users can turn on the option for each paired watch after entering the phone’s passcode.
Series 9, Ultra 2 and SE 3 watches qualify, and the watch must be worn, unlocked and near the phone for authentication to work reliably.
Users still need to wake the device and swipe up past the Lock Screen, though Apple allows that extra swipe step to be disabled in Settings.