Biometrics: what survives a repair and what does not
The short answer
Face unlock uses a sensor array in the top of the screen assembly, which is transferred to a new panel rather than replaced. Fingerprint readers are paired to secure hardware on the board and generally cannot be replaced by anyone outside the manufacturer. Both survive a properly done screen repair.
How face unlock actually works
The good implementations are not a camera looking at a photograph. A projector throws thousands of invisible infrared dots onto your face, an infrared camera reads how that pattern distorts across the shape of it, and the device builds a depth map. A flood illuminator lets it work in the dark.
That depth map is turned into a mathematical representation and stored in dedicated secure hardware on the board, not in a file and not in the cloud. It never leaves the device and it cannot be read back out as a picture of you.
Cheaper face unlock on some phones is a camera and software, which is convenient and much easier to fool with a photograph. It is worth knowing which your phone has before relying on it for banking.
Why it survives a screen repair, when done right
The sensor array sits along the top edge of the display assembly. A replacement panel does not come with your array, and your array is registered to your board's secure hardware, so it is carefully transferred from the old screen to the new one.
Done properly, face unlock works exactly as before and nothing is re-registered. Done in a hurry, a flex gets torn or a connector is not seated, and the phone reports that face unlock is unavailable. That is the failure mode people warn about, and it is a workmanship problem rather than an inevitability.
It is one of the things we test before a phone goes back, because it is the fault most likely to be discovered on the walk home.
Fingerprint readers are a harder case
A fingerprint reader is paired to the secure hardware on the board at manufacture, and on most phones it genuinely cannot be replaced independently. Fit a new one and it simply will not authenticate, because the pairing is the security.
Where the reader sits under the display, a screen replacement has to account for it. On phones with an ultrasonic reader, which reads the ridges of your finger with sound rather than light, the sensor is calibrated to the panel it shipped with, and a replacement panel means recalibration or a reader that no longer recognises you.
On phones with the reader in the side button or on the back, it is usually unaffected by a screen repair entirely.
This is the honest limit of independent repair and we would rather state it plainly. If your fingerprint reader itself has failed, the answer on most phones is that nobody outside the manufacturer can replace it.
- Under-display optical readers: usually survive a screen repair, sometimes need re-registering
- Under-display ultrasonic readers: calibrated to the panel, and a replacement has to account for it
- Side-button and rear readers: generally unaffected by a screen repair
- A failed reader itself: on most phones, not independently replaceable
After a repair
- Test it before you leaveWe test it, and you should too. It is easier to sort at the counter than at home.
- Re-register if askedSome phones want the fingerprint enrolled again after a screen replacement. That is normal and takes a minute.
- Expect a parts notice on some modelsA phone can report an unverified display and still have perfectly working biometrics. Those are separate things.
- Tell us if it was already failingA biometric that stopped before the repair is a different conversation from one that stopped after, and knowing which changes what we check.
What we will not do
Disable a security feature to make a part work. If a screen needs face unlock turned off to avoid a warning, the screen is wrong.
Promise a biometric will survive when the hardware itself is what failed. If your sensor array is damaged rather than your panel, we will say so before quoting a screen.
Or fit a replacement fingerprint reader on a phone where it cannot authenticate afterwards, which would mean selling somebody a part that does nothing.
Common questions.
Yes, when the job is done properly. The sensor array is yours and is transferred from the old screen to the new one. It fails when that transfer is rushed, which is a workmanship problem rather than a rule.
On most phones, no. The reader is paired to secure hardware on the board at manufacture and a replacement will not authenticate. We will tell you that rather than fit a part that does nothing.
Sometimes, on phones with an under-display reader. It takes a minute and it is normal rather than a sign anything went wrong.
It is stored as a mathematical representation in dedicated secure hardware on your device. It does not leave the phone, it is not a picture, and a repair does not give anybody access to it.
No. Camera-only face unlock has no depth information and is much easier to fool. If your phone offers a fingerprint or a passcode for banking, use that instead.
Where this leads.
Next in locks and security.
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