The Galaxy S20 has an ultrasonic fingerprint sensor under the screen and face recognition, and six years after its launch, unlock problems on it are mostly protectors, worn registrations and the age of the phone. The sensor sits in the lower part of the 6.2 inch display. An ultrasonic reader works through the glass but needs a clear contact, so a protector that was not designed for it, or one that has air under it or has cracked over the sensor, will block it. Remove the protector to test; if the problem goes, fit a protector designed for the S20's sensor and register your finger again.
Clean the screen and your finger, since grease and moisture reduce readings. Go to Settings, Biometrics and security, Fingerprints, enter the PIN and see what is registered.
The checks in more detail
Delete a fingerprint that fails often and register it again, pressing flat and covering the sensor, and register the same finger twice and a second finger as a backup. Over years, skin changes, and a registration made in the first year may need renewing. Check that Unlock phone is on. Face recognition, in the same menu, is a convenience that Samsung rates as less secure and that fails in dim light. The S20 is on its final software, so no new fixes will arrive, and its battery may be weak. A swollen battery can lift the screen and disturb the sensor, so check that the display is flat; if it is lifting, stop using the phone and have it repaired.
If you replaced the screen, an uncalibrated display may stop the reader enrolling. Restart the phone and run Samsung Members diagnostics. If the sensor does not respond after these steps, contact Samsung or a repairer with the serial number, and consider whether a battery replacement or a new phone is the better value. Keep the PIN safe, since it is the fallback. Because the S20 is one of the oldest phones still in use with an ultrasonic reader, its owners often meet a quirk that newer ones avoid: Samsung's Touch Sensitivity option, in Settings, Display, which makes the touch layer more responsive for screen protectors, can interfere with the fingerprint sensor on some builds, so toggle it off as a test.
The S20 also has a 120 hertz screen that can be switched to 60, and a very bright or dim screen changes how the sensor behaves in sunlight, so test indoors. Remember that this phone has stopped receiving updates, so a fault caused by software will not be repaired by Samsung and the answer is a setting change, a reset or a replacement.
Because the S20 had separate versions with different chips, some S20 phones have slightly different sensor firmware, and the symptoms differ with the model. If you bought it second-hand, ask whether the screen was ever replaced, and check the date of the last security patch in Settings, About phone, Software information. A fresh start sometimes clears odd behavior: back up and reset only if everything else has failed, and if you do, register the fingerprints first thing after setup, before installing apps.
Differential
Likely causes of “Samsung Galaxy S20 family biometric unlock is not working”, and how to tell them apart
- 1
A screen replaced without calibration
What separates it The reader will not enrol
How to confirm Have it calibrated
- 2
Dim light for face unlock
What separates it Face recognition fails
How to confirm Use the fingerprint
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether a protector is fitted
- Whether the screen was replaced
Try in this order
0 of 3 completedCheck the screen is flat
ReversibleSwollen battery.
Restart and run diagnostics
ReversibleSamsung Members.
Keep the passcode working
ReversibleCheck that you remember your PIN or password before you delete and register fingerprints again, so a failed reader never locks you out. You can review both under Settings, Biometrics and security.
Model-specific
What is true of this model and not of its siblings
- Ultrasonic
- It reads through glass.
- Age
- The phone is six years old.
Stop boundary
When this stops being a self-service repair
- !If the sensor does not respond, contact Samsung or a repairer with the serial number
- !Stop using a swollen phone
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Is the S20 still supported?+
It is on its final software.
Why does my S20 fingerprint fail?+
A protector or an old registration.
What if the S20 fingerprint reader stopped after a screen replacement?+
The in-display reader sits behind the glass, so a replacement screen or a damaged one can leave it unable to read. Use your PIN or password in the meantime and have the screen checked by a Samsung service center rather than re-registering fingers again and again.