Samsung Galaxy S21+ biometric unlock is not working

The checks in more detail

Take the protector off to test, then, if you want one, choose a protector made to work with the S21+ sensor and register your fingerprint again after fitting it. Open Settings, Biometrics and security, Fingerprints, enter the PIN and look at what is registered. Delete a print that has become unreliable and add it afresh, covering the whole sensor with the finger pressed flat, and register the same finger twice from slightly different angles, with a second finger as a backup.

Over years of use, skin changes, and a registration that worked in the first year may need renewing. Check that Unlock phone is on and that fingerprint verification is enabled in the apps that use it. Face recognition, in the same menu, is a convenience that Samsung rates as less secure. If the sensor stopped reading after a screen repair, the replacement display may not have been calibrated, and an unofficial repair can leave the reader unable to enrol; Samsung or a repairer with the right tools can fix that.

Update the software, restart, and run the diagnostics in Samsung Members. A phone that asks for the PIN after a restart or several failed attempts is behaving normally. If the sensor does not respond at all after a protector check, a registration and a restart, contact Samsung with the serial number. Remember the PIN, since it is always the fallback. The S21+ shipped with a factory screen protector film already applied, and when that film peels, bubbles or is replaced with a thick glass protector,

the sensor often stops working, which is the most common story among owners of this model. If the film has begun to lift at the edges, peel it and fit a protector that explicitly supports the in-display sensor, then register again. Samsung's Members app runs a sensor test on the S21+ that shows whether the reader gets a signal at all, which separates a protector problem from a hardware one. A phone from early 2021 may also have a battery that has swollen slightly; if the screen is lifting, stop using it.

The seven-year age of the design means the registration data can be stale, so renewing prints is worth doing once a year. Owners who bought the S21+ new usually had a pre-applied film that peels at the corners after a year or so; remove it fully rather than letting it sit half off, because a partly lifted film traps air over the sensor. A glass protector that includes a cut-out or a special sensor area may be required for some brands; read the packet's compatibility list for the S21+ by name.

If you use a case with a magnetic ring, take it off for the test, because a metal ring near the sensor area can affect readings. The Galaxy S21+ has an under-display fingerprint sensor that uses ultrasound, and it reads best when the finger is clean, dry and covers the whole sensor area. Wash and dry your hands, wipe the area of the screen with a soft cloth, and if you use a screen protector, check that it is one made for ultrasonic sensors; some thick or air-gapped protectors stop the sensor reading.

Register the same finger twice as two entries to improve recognition, and add the edge of the finger. In Settings, under Biometrics, the Fingerprint settings include a setting for higher touch sensitivity, which helps with a protector. Face unlock on this phone uses the front camera and is less secure than the fingerprint; if it fails, check that the camera is clean and that Face recognition is not turned off. If neither works after a restart, a software update can fix a bug.