Owners of Xiaomi and Redmi smartphones often face a situation where biometric protection suddenly ceases to function, blocking quick access to the device. This can happen at any time: after another system update, a gadget crash or a spontaneous failure in the operation of the TEE security module (Trusted Execution Environment).
There are many factors that affect the stability of the scanner, from the banal dirt on the surface to serious hardware damage to the plume. In this article, we will discuss in detail the software and physical causes of malfunctions, as well as provide step-by-step instructions for restoring the sensor to health. It is important to understand that in most cases, the problem can be solved independently without resorting to the services of a service center.
If your Redmi Note or Poco has stopped seeing your finger, don't rush to carry it for repair. Often, simply calibrating or resetting your biometrics settings is enough. Let's look at the basic breakdown scenarios and effective methods to fix them to get your device back to its previous speed and safety.
The main reasons for failure of biometric protection
The first priority is to identify the root of the problem, because the next algorithm of actions depends on it. Most often, the scanner's malfunction is associated with software conflicts in the MIUI or HyperOS shell. After a major operating system update, old biometric data can conflict with new drivers, causing recognition failures.
Physical damage is also a leading cause, and even a micro-crack on the sensor's protective glass or moisture entering the body can disrupt sensor contact with the motherboard, and it's important to know that ultraviolet radiation and extreme temperatures can irreversibly damage the sensor's sensitive element.
Also, the condition of the finger should be considered: too dry skin, the presence of cuts, calluses or residues of the cream significantly reduce the quality of reading the picture. In some cases, the security system blocks the entry attempts after several unsuccessful attempts, requiring input. PIN-code for re-activation of the module.
⚠️ Note: If the smartphone has recently undergone unqualified repair or replacement of the display, the problem may lie in a poor quality plume or lack of calibration of the new module.
Programmatic methods of troubleshooting
The first step is to start a diagnostics process with the software part, because it's the least risky and fastest way to do it, and the first step is to completely remove your previously stored fingerprints and re-register them, which allows you to update your digital finger card in the system's memory and eliminate read errors.
To perform this operation, go to the Settings menu → Passwords and security → Fingerprints. Delete all saved profiles and add a new one, following the instructions on the screen carefully. When registering again, try to touch the sensor with different parts of your finger to create the most complete digital cast.
If simple deletion didn’t work, try resetting the Security app settings or clearing the cache of the system services responsible for biometrics. Sometimes background processes freeze and stop processing sensor signals correctly. Rebooting the device in safe mode can also help identify a conflicting third-party application.
☑️ Diagnostics PO
Hardware problems and physical impact
When software methods fail, attention shifts to hardware. Fingerprint scanners, especially those embedded in the screen (Under-Display), are extremely sensitive to the quality of protective glass and film. Thick protective glass or film with poor light transmission can block the optical signal, making the scanner unworkable.
Mechanical impacts and falls often result in detachment of the plume connecting the scanner module to the main board. In models with a side scanner combined with the on button, the problem can be related to wear of the button mechanism itself. Internal oxidation of contacts due to moisture is also a common cause of failure.
To check the hardware, you can use the Xiaomi engineering menu. Type ##6484## in the phone app to enter CIT (Customer Interface Test) mode. Choose Fingerprint test and follow the instructions. If the scanner is not responding in this mode, the probability of hardware failure is as high as 90%.
How do I check the scanner plume?
The effect of protective accessories on the operation of the sensor
Many users forget that accessories designed to protect a smartphone can cause it to malfunction, especially for optical scanners built into the display, any barrier between the finger and the sensor distorts the light flux needed to build an image of the fingerprint.
If you use a security glass, make sure it has a special notch under the scanner or is marked as compatible with Screen Fingerprint technology. Cheap glasses can have uneven thickness or low transparency in the sensor area, making recognition impossible.
Dirt, greasy spots and dust on the surface of the screen or the sensor itself (if located on the back) are also critical. Regularly cleaning the scanning area with a soft microfiber can instantly solve the device's "blindness" problem.
Comparison of scanner types and their vulnerabilities
Understanding the type of scanner you have installed on your device helps you diagnose the problem more accurately. Xiaomi and Redmi use three main types of sensors, each with its own weaknesses and operating features.
| Type of scanner | Principle of work | Frequent problems | Sensitivity |
|---|---|---|---|
| Optical (in screen) | Light scanning | Reacts to brightness, film. | High to pollution |
| Capacitive (back/side) | Skin current response | Dry fingers, water, cracks | Moisture-average |
| Ultrasonic. | 3D Sound Waves | Rare software failures, thick glass | Low (works in water) |
Optical scanners, which glow green when you put your finger on, often "glut" when the screen is low or in high sun. Capacitive sensors located on the end or back may stop working if you use your smartphone with gloves or wet hands.
Ultrasonic scanners are less common, mostly in flagship models, and are considered the most reliable, but even they can fail when using certain types of protective glasses that do not allow ultrasound to pass.
Sensitivity setting and re-registration
If the scanner works but often fails, it may be worth improving the quality of fingerprint preservation, allowing multiple copies of the same finger to be saved under different names, which increases the likelihood of successful unlocking.
Try registering the same finger twice, once as Finger 1 and again as Finger 2. When registering for the second time, click on the sensor a little bit from a different angle or use a different part of the pad, which will expand the database for comparison.
Some firmware versions also offer a "High Sensitivity" setting (often used with film) that you can turn on in your fingerprint settings if the standard mode is no longer working, but be prepared for the fact that false positives may become more frequent.
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When registering a fingerprint, don't hold your finger statically. Move it a little bit, change the angle of inclination, and apply different areas of the pad to create a more complete profile.
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Re-registration of the fingerprint with different touch angles solves the problem of recognition in 70% of cases of software failures.