Why iPhone Duo Uses Touch ID: What Changes Without Face ID

Why a side sensor suits a foldable

A side button is reachable when the phone is closed, partly open or flat. Camera-based authentication has to work across displays and orientations, while a physical sensor stays in one predictable location.

Everyday differences

Touch ID can be convenient on a desk or while wearing a face covering. Wet fingers, gloves and a poorly registered finger edge can cause failures. Register fingers that naturally reach the button in both hands rather than only one thumb.

For first-day settings, follow our setup checklist.

Purchases and passwords

The authorization method changes, but the flow remains familiar: confirm with the enrolled biometric and use the passcode fallback. Practice the button position before relying on it at a checkout.

Users with limited reach should test which finger works across folded and unfolded positions. Never add another person’s fingerprint to simplify sharing.

Touch ID is neither automatically better nor worse than Face ID. It is a different interaction suited to a multi-position device. See is iPhone Duo worth it? for the complete decision and our tutorials for practical guidance.