Owners of Xiaomi, Redmi and POCO smartphones often encounter a mysterious message in system logs or an engineering menu called sarsensor.This term can scare the inexperienced user, evoking associations with viruses or critical system errors, but in fact everything is much more prosaic. Sarsensor is a software identifier of the proximity sensor, which plays a key role in everyday use of the gadget.
This is the component that automatically shuts down the display during a phone call when you hold your smartphone to your ear. Without the proper operation of the sarsensor, the screen would continue to burn, leading to accidental cheek or ear pressing, a call reset or hands-free operation. Understanding how this module works will help quickly diagnose and eliminate common problems with touchscreen and calls.
Principle of operation and purpose of the proximity sensor
The proximity sensor, which is referred to as sarsensor in the system, is an infrared emitter and receiver located at the top of the smartphone body, and its main task is to measure the distance to the nearest object. When you make a call and hold the phone to your head, the sensor detects the change in distance and sends a signal to the MIUI or HyperOS operating system to quench the screen.
Once the conversation is over or the device is removed from the ear, the sarsensor activates the display again.This not only prevents false positives, but also significantly saves battery power, since the screen is one of the main consumers of energy. In some Xiaomi models, this sensor is also used for smart functions, such as lifting the phone to activate the screen or controlling gestures.
It is important to note that modern Xiaomi smartphones use two types of sensors: classic, located in a narrow frame above the screen, and virtual, built directly into the display matrix. Virtual sensors are often called ultrasonic proximity sensor, and they require more complex software calibration for accurate operation.
⚠️ Warning: If you have a black-framed protective glass or film that is too thick, it can block the work of sarsensor, causing constant screen failures during calls.
Why does the screen go out when you call Xiaomi?
The most common user complaint related to sarsensor is that the screen does not go out during a conversation, which leads to the user accidentally pressing volume buttons, completing a call or turning on the speaker while pressing the phone against the cheek, for several reasons, and most of them are solved by software methods.
Often the problem is that the dust, the fat from the fingers, or the glue from the previous protective glass interferes with the infrared beam, in which case the sarsensor thinks that the object (your ear) is already nearby, and either keeps the screen off permanently or cannot be calibrated correctly.
Another cause is software conflicts: after updating the MIUI firmware, calibration settings may be lost, and third-party applications that intercept sensor control, or cache of system services, may also be affected, and in rare cases, it is a physical damage to the plume or the module itself after falling or getting moisture.
- 📱 Pollution of the top of the screen with dust or fat.
- 🛡️ Inappropriate protective glass covering the sensor.
- 🔄 Errors in the firmware after the system update.
- 🔋 Failures in the operation of the communication module or radio module.
Diagnosis and performance testing
Before you carry your smartphone to the service center, you need to conduct a self-diagnosis. Xiaomi’s shell has a powerful CIT (Customer Inspection Test) engineering tool that allows you to check all hardware components, including sarsensor. To start the diagnosis, open the Phone application and type the combination ##6484#.
In the menu that opens, look for the Proximity Sensor or Light & Proximity Sensor, and if you click on it, you'll see the current readings of the sensor, hold your palm to the top of the screen and remove it, and if the numbers change (usually from 5.0 to 0.0 or vice versa), then the part is good, and the problem should be looked for in the software.
If the values do not change at all or the sensor shows a constant value "close", even when there is nothing in front of the screen, this may indicate a physical failure or a critical failure of the drivers, in which case the software calibration may not help.
Calibration methods for the proximity sensor
If the diagnostics show that the sensor is working but it's not working properly, you need to calibrate the sarsensor, which is the process of "training" the system to the correct distance values, and on Xiaomi smartphones, you can do this through the engineering menu that we opened earlier.
In the CIT menu, select Proximity Sensor. You will see a two-button window. First, remove your hand from the screen to let the sensor show "Far" (far away), and press the Pass or Calibrate button. Then close the sensor tightly with your palm (near or close should appear) and press the confirmation button again. After passing the test, the system will save the new reference values.
There is also an alternative method through a hidden menu of engineering settings. To do this, enter the code # # #64663## in the Phone app (code may vary depending on the model and version of MIUI). In some cases, resetting all settings to factory settings helps, but this is an extreme measure that requires prior data backup.
Comparison of sensor types in Xiaomi models
Xiaomi’s different smartphone models come with different approximation sensor modifications that affect accuracy and troubleshooting techniques. Understanding which type is installed on your device helps you choose the right repair or setup strategy.
Classic infrared sensors that are framed are more susceptible to contamination, but easier to calibrate. Ultrasonic and optical sensors under the screen are less visible, but sensitive to the quality of protective glasses and software bugs.
| Type of sensor | Location. | Sensitivity | Typical problems |
|---|---|---|---|
| Infrared (IR) | Frame above the screen | Medium | Pollution, dust in dynamics |
| Optical (under the screen) | Under the display matrix | Tall. | Films, firmware bugs. |
| Ultrasonic. | Corps/Screen | Very high. | Covers, physical damage. |
| Virtual (AI) | Software | Depends on the software. | False positives |
Solving problems with third-party software
When Xiaomi’s regular funds fail, apps from the Google Play Store come to the rescue. There are utilities like Proximity Sensor Reset or Sensor Box that allow you to perform deep calibration or temporarily disable the sensor if it doesn’t work properly.
Some users prefer to use the In-Pack mode, which locks the screen when closing the upper left corner, ignoring the main proximity sensor. This solution is relevant for models with known sensor hardware problems, such as some versions of the Redmi Note. To activate, go to Settings → Lock and Protection → Mode in your pocket.
It's important to understand that installing sarsensor control applications is a temporary solution, so if the sensor is physically defective, no application will make it work perfectly, and in such cases, it's best to contact a specialist to replace the plume or module.
⚠️ Warning: When installing sensor calibration apps, read reviews carefully. Many of them contain aggressive advertising or may collect data about your device.
Impact of MIUI and HyperOS updates on sensors
Xiaomi regularly releases updates for its devices, which often contain driver error corrections, but the opposite happens: after updating MIUI or switching to HyperOS, users begin to notice strange behavior of the proximity sensor, which is due to a change in data processing algorithms.
Developers can change sensitivity thresholds to reduce false positives, but as a result, the sensor becomes less responsive.If the problem appears immediately after the update, it makes sense to wait for the patch to come out or perform a full reset (with a backup) to eliminate conflicts of old configuration files.
Owners of Root devices can edit the system files that calibrate sarsensor, but this requires deep technical knowledge.