Refurbished iPhone Face ID Guide: Sensor, Portrait & Attention Checks

Meta description: A practical iPhone Face ID test for refurbished iPhones, covering sensor checks, Portrait mode depth, attention features, and what to do if anything fails.

Buying refurbished iPhones is a bit like buying a used car: the paintwork matters, but you really want to know the engine starts every time. With iPhones, Face ID is that “turn the key” moment. If it’s flaky, daily life gets annoying fast, unlocking, banking apps, and even password autofill.

This guide gives you a fast, real-world iPhone Face ID test you can run in minutes, whether you’re checking used iPhones in person or unboxing cheap iPhones that just landed on your doorstep. You’ll also check Portrait mode depth and the attention features that stop your phone unlocking when you’re not looking.

If you’re browsing Used Mobiles 4U for iPhones for sale, keep this page open and test as you go.

Before you run an iPhone Face ID test: 2-minute prep that prevents false fails

Face ID problems are often simple. A smudge, a thick screen protector, or a case lip can make a perfectly good phone look broken. Start with a clean slate so your results mean something.

First, wipe the top front of the phone (the area around the earpiece) with a dry microfibre cloth. Don’t use sprays or wipes that leave a film. If there’s a screen protector fitted, check it isn’t chipped or lifting right near the sensors. A tiny crack in the wrong spot can throw Face ID off, the way a dirty pair of glasses can make the world feel fuzzy.

Next, remove any bulky case and test in steady indoor light. Face ID uses infrared too, but you still want a calm setup, not bright sun behind you or a dark room.

Now check the basics:

• Open Settings > General > Software Update and install the latest iOS available.
• Restart the phone (a simple reboot fixes more than people expect).
• Make sure you know the passcode. You’ll need it to change Face ID settings.

If you’re buying second-hand iPhones, it’s also worth doing a wider health check (buttons, speakers, charging, cameras). This broader checklist helps you catch “good Face ID, bad everything else” situations, see Laptop Outlet’s refurbished phone checks.

The iPhone Face ID test: quick sensor checks that reveal most issues

Here’s the fastest way to judge whether the TrueDepth system is behaving normally, without any special apps.

Step 1: Can Face ID enrol your face without errors?

Go to Settings > Face ID & Passcode, enter the passcode, then tap Set Up Face ID (or Reset Face ID if it’s already set). Enrolment is a strong test because the phone has to “see” depth, track movement, and build a consistent map.

As you do the two scans, watch for these signals:

• Good sign: the circle fills smoothly, and you’re done in under a minute.
• Worry sign: repeated “Move iPhone lower/higher” loops even when you’re centred.
• Bad sign: “Face ID is not available” or “Unable to activate Face ID” during set-up.

If enrolment fails, stop and re-clean the sensor area once. If it fails again, treat it as a return-worthy fault on a refurbished unit.

For a plain-English explanation of what’s inside that sensor array, Apple’s overview of Face ID advanced technology is useful context.

Step 2: Test real unlocking, not just set-up

After set-up, lock the phone, wake it, then look at it naturally from about an arm’s length. It should unlock with a quick glance, not a stare-down.

Do three practical checks:

1. Normal unlock: wake, look, swipe up.
2. Angle check: hold it slightly lower, like you would on the sofa.
3. Low-light check: try in a dimmer room (not pitch black).

If it only works when you hold it “perfectly”, that’s not normal behaviour. It’s the phone equivalent of a car that only starts if you jiggle the key.

Step 3: Attention settings, the “eyes open” test

In Settings > Face ID & Passcode, toggle Require Attention for Face ID on. Now try unlocking with your eyes closed (it should fail). Open your eyes and try again (it should work).

This one test tells you a lot. If Face ID unlocks with eyes closed while attention is required, something’s off. If it never unlocks with attention on but works when attention is off, the phone may struggle to track your gaze, or you may need to re-enrol in better light.

Apple’s guide to Face ID and attention settings shows where these options live if the menus look different on your iOS version.

Portrait mode and attention-aware features: checks people forget until it’s too late

Face ID isn’t only for unlocking. The same front sensor system also supports depth effects and attention tools. If you want the phone to feel “proper”, test the features that rely on that depth data.

Portrait mode: check depth looks clean, not cut-out

Open the Camera app and switch to Portrait. Stand a couple of metres from a person (or use a chair with clear edges). You’re looking for smooth separation between subject and background.

Take a few shots and zoom in on:

• Hair edges (a common weak spot if depth data is messy).
• Glasses frames (shouldn’t vanish into blur).
• Background blur (should look gradual, not like a sticker outline).

If Portrait mode refuses to engage, or the blur looks glitchy and inconsistent, that can point to sensor issues or a poor-quality past repair. Apple’s basics on using Portrait mode can help you confirm what “normal” looks like for your model.

Attention-aware features: the everyday feel test

In the same Face ID settings screen, enable Attention Aware Features. Then do something simple:

• Start playing audio at a comfortable volume.
• Look at the screen, then look away.

On supported models, the phone should react to your attention in small ways (like lowering alert volume when you’re looking). These are subtle, but when they’re missing, the device can feel oddly “deaf” to you.

A quick reality check: if you wear polarised sunglasses, Face ID can struggle in bright conditions. Test without them to avoid blaming the phone for your lenses.

A note for bargain hunters choosing between platforms

If Face ID is a must-have, Cheap Android Phones won’t always give you an equivalent experience. Many Androids use fingerprint readers or 2D face unlock. That’s not bad, it’s just different. If you’re considering a used Samsung, check what biometric method it uses and whether it fits your routine (gloves, masks, commuting, night use).

Wrap-up, plus FAQs to keep in your pocket

A good iPhone should unlock like it knows you, fast, boring, and reliable. If your iPhone Face ID test shows set-up errors, patchy attention behaviour, or Portrait depth that looks wrong, don’t talk yourself into living with it. With refurbished devices, the whole point is value without daily friction.

If you’re upgrading, consider the greener exit too: sell your tech, sell old iPhone, or trade-in iPhone rather than leaving it in a drawer. If you’re thinking “should I recycle my old iPhone or trade-in my old phone?”, pick the option that keeps it in use longest, then recycle as the final step.

FAQs

Why does Face ID fail on used iPhones after a repair?

Face ID relies on the TrueDepth system. Some screen or front sensor repairs can disturb alignment or damage parts, causing set-up failures or unreliable unlocking.

Can a screen protector break Face ID?

A good one usually won’t, but a cracked, poorly fitted, or thick protector that covers the sensor area can cause failures. Remove it and re-test before deciding it’s a fault.

How do I test Face ID quickly when collecting a phone in person?

Do Face ID enrolment, do one normal unlock, then enable “Require Attention” and try the eyes-closed test. That trio catches most problems in under five minutes.

Is Portrait mode a reliable sign the sensors are healthy?

It’s a strong clue, especially front Portrait. If depth edges look messy or Portrait won’t engage, it can point to sensor or repair issues worth taking seriously.

I want cheap iPhones, but I also want peace of mind. What should I look for?

Prioritise warranty, returns, and evidence of testing. The best deals on iPhones for sale are the ones you can send back if Face ID or the cameras don’t match the description.