This is a very strange issue I'm having. I have an LG K40S with Android 10 and a couple of days ago I started having problems unlocking its screen. Neither the power button nor the biometrics sensor will unlock it. I can only manage to do it by pushing the power button several times, which opens the camera, then I can unlock it. Today, I realized this only happens when I'm in my room at night with the lights off (or anywhere dark, for that matter). When there's enough light I can unlock it just fine. If I cover the sensor with my finger the screen can't get unlocked again.

This started heppening after I dropped my phone, could it be that the light sensor is broken somehow? The screen auto brightness seems to be working, so maybe there's nothing wrong with sensor. I tried going into developer mode and disbale the sensor but that option is not available on my phone.

Please, any help or insight into this issue is much appreciated. Thank you very much!

  • Thank you, that was exactly what was going on! I dind't even think about the proximity sensor, but after running a test app, sure enough, it showed the sensor was detecting proximity whenever there was low light. I realized the screen protector was also responsible for this malfunction (maybe after I dropped the phone the sensor couldn't properly "see" through the protector anymore). I just removed the screen protector and now everything is working fine. Thank you again the help! Commented Feb 10, 2022 at 15:12
  • I converted my comment into an answer so you can accept it.
    – Robert
    Commented Feb 10, 2022 at 15:43

1 Answer 1


Phones have a second light based sensor: the sensor that detects if you hold your phone near the face while a phone call (often called proximity sensor).

If it detects you are close the screen the screen stays off, therefore a defect or some other problem that prevents this sensor from working properly could explain your problems.

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