The short version
- iPhone Duo has four ambient light sensors. iPhone 18 Pro Max has dual ambient light sensors.
- iPhone Duo uses Touch ID for fingerprint authentication. iPhone 18 Pro Max uses Face ID.
- iPhone 18 Pro Max includes a LiDAR Scanner.
Both phones publish a Sensors list on their tech specs pages. The two lists differ in three entries: the ambient light sensors, the biometric hardware, and the LiDAR Scanner.
iPhone Duo and iPhone 18 Pro Max sensor lists
Every entry in the Sensors category
| iPhone Duo | iPhone 18 Pro Max |
|---|---|
| Touch ID fingerprint sensor | Face ID |
| Barometer | Barometer |
| High dynamic range gyro | High dynamic range gyro |
| High-g accelerometer | High-g accelerometer |
| Proximity sensor | Proximity sensor |
| Four ambient light sensors | Dual ambient light sensors |
| — | LiDAR Scanner |
Camera specifications, Location, and MagSafe and Wireless Charging occupy separate categories, so the number of entries does not represent every sensing component inside either phone.
Sensor browser: filter the Sensors entries Apple lists for iPhone Duo and iPhone 18 Pro Max, then open an entry to read what Apple says it is and what it enables.
Both phones also have a digital compass under Location and a magnetometer under MagSafe and Wireless Charging.
Display features alongside ambient light sensing
iPhone Duo has an inner folding display and an outer display. Both are Super Retina XDR OLED displays, as is the display on iPhone 18 Pro Max.
Screen sizes, features, and brightness
| Display specification | iPhone Duo | iPhone 18 Pro Max |
|---|---|---|
| Display size, diagonal | 7.6-inch inner; 5.4-inch outer | 6.9-inch |
| True Tone | Both displays: supported | Supported |
| Always-On display | Both displays: supported | Supported |
| ProMotion | Both displays: ProMotion technology with adaptive refresh rates up to 120Hz | ProMotion technology with adaptive refresh rates up to 120Hz |
| Typical brightness | Both displays: 1000 nits max brightness (typical) | 1000 nits max brightness (typical) |
| HDR brightness | Both displays: 1600 nits peak brightness (HDR) | 1600 nits peak brightness (HDR) |
| Outdoor brightness | Both displays: 3000 nits peak brightness (outdoor) | 3000 nits peak brightness (outdoor) |
| Minimum brightness | Both displays: 1 nit minimum brightness | 1 nit minimum brightness |
The inner display on iPhone Duo has a nano-texture finish. Apple says it reduces glare and reflections.
Apple also lists Wide-angle OLEDs on the inner display, which it says are for optimal visibility.
iPhone Duo and iPhone 18 Pro Max both support Crash Detection.
Apple describes the feature as using hardware sensors and advanced motion algorithms to detect a severe car crash and call for help if you cannot.
Touch ID with iPhone Duo open or closed
iPhone Duo integrates its Touch ID fingerprint sensor into the side button.
You can use Touch ID whether the phone is closed or open.
Face ID and the front cameras
On iPhone 18 Pro Max, TrueDepth technology in the Center Stage front camera enables Face ID.
Front camera hardware by position
| Front camera | Specification |
|---|---|
| iPhone Duo: Outer | 12MP Center Stage camera |
| iPhone Duo: Inner | Under-display FaceTime camera |
| iPhone 18 Pro Max | 18MP Center Stage camera |
The inner camera on iPhone Duo supports Center Stage for video calls. It sits beneath the display and stays hidden when not in use.
You can take FaceTime calls while holding iPhone Duo open or prop it on a surface for hands-free FaceTime.
Apple Pay and Apple Watch unlock
Apple Pay uses each phone’s biometric authentication method for purchases in stores, within apps, and on the web.
Payment authentication and supported uses
| Apple Pay use | iPhone Duo | iPhone 18 Pro Max |
|---|---|---|
| Purchases in stores, within apps, and on the web | Touch ID | Face ID |
| Complete purchases made with Apple Pay on a Mac | Supported | Supported |
| Pay for rides using Express Transit | Supported | Supported |
Apple separately states that you can unlock iPhone Duo using an Apple Watch.
FAQs
Why do the precise display diagonals differ from the advertised sizes?
The advertised sizes are rounded. Measured as standard rectangles, iPhone Duo’s inner display is 7.58 inches diagonally and its outer display is 5.36 inches. The iPhone 18 Pro Max display measures 6.86 inches. Each screen has rounded corners within that rectangle, so its actual viewable area is smaller.
What connection does Crash Detection require to call for help?
Crash Detection requires a cellular connection, satellite connectivity, or Wi-Fi calling to call for help.
Is Express Transit available everywhere?
No. Express Transit is available only in select cities and transit systems. It also requires an eligible device and OS version.
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