The Galaxy S25 unlocks with an under-display ultrasonic fingerprint reader, and with face recognition as a convenience option. The ultrasonic reader reads the ridges of your finger in three dimensions through the glass, which is why it still works with a slightly damp finger but not with a screen protector that was never made for it. When the fingerprint starts to fail, think of the protector first, then of a stale registration, then of the moisture or oil on your finger, and only then of the sensor itself. Re-adding the print takes a minute and cures most cases.
Differential
Likely causes of “Samsung Galaxy S25 biometric unlock is not working”, and how to tell them apart
- 1
A screen protector that was not made for ultrasonic readers
What separates it The fingerprint failed the day a new protector went on
How to confirm Peel it off and try; if the reader works, replace it with one rated for the S25
- 2
A fingerprint registration that has aged
What separates it The reader needs several tries more often than a month ago
How to confirm Settings, Biometrics and security, Fingerprints: delete the print and add it again, pressing the way you hold the phone
- 3
Oil, dirt or heavy moisture on the finger or the glass
What separates it It fails after cooking, the gym or a shower
How to confirm Wipe the screen and your finger dry, then try again
- 4
Face recognition in poor light
What separates it Face unlock fails in a dark room or with glasses
How to confirm Use the fingerprint, and re-register the face in a lit room
- 5
A software glitch after an update
What separates it The reader stopped after an update with no change to the protector
How to confirm Restart, install the newest patch, then re-add the print
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the fingerprint, the face unlock, or both fail
- The protector brand and when it was fitted
- When it started and whether an update came first
- The One UI version and security patch date
Try in this order
0 of 6 completedClean and dry
ReversibleWipe the screen and your finger with a dry cloth so the reader sees clean ridges.
Take the protector off to test
ReversiblePeel the protector and try the fingerprint. If it works, the protector was blocking it.
Add the print again
ReversibleSettings, Biometrics and security, Fingerprints. Delete the old print and add the finger, covering the whole fingertip and holding the phone the way you normally do.
Add a second copy
ReversibleRegister the same finger twice so the phone has a second reference at a slightly different angle.
Restart and update
ReversibleRestart, then install the newest patch under Software update.
Test in Safe mode
ReversibleHold the power key, touch and hold Power off and choose Safe mode to rule out an app that interferes with the lock screen.
Model-specific
What is true of this model and not of its siblings
- Ultrasonic versus optical
- An ultrasonic reader sends a sound pulse and reads the echo off your ridges, so it copes better than an optical reader with wet or dusty fingers but depends on a clean glass-to-skin contact.
- Where the reader is
- Low on the screen, roughly where your thumb rests when you hold the phone; a crack in that area is a display repair.
Stop boundary
When this stops being a self-service repair
- !If the reader fails with no protector and after a re-registration, book a Samsung repair
- !If the screen is cracked near the reader, the display needs repairing
- !If only face unlock fails, test the front camera in the Camera app
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Which fingerprint sensor does the Galaxy S25 use?+
An under-display ultrasonic reader, which reads ridges in three dimensions through the glass.
Why did my fingerprint fail after a new screen protector?+
The protector can block the ultrasonic signal. Use one made for the S25's reader.
Is face unlock as secure as the fingerprint?+
Samsung's face unlock is a convenience level; use the fingerprint for payments and banking.
Can I register the same finger twice?+
Yes, and it improves reliability.