iphone screen goes black during phone calls when trying to type on keypad

When making a call on my iPhone 4 (iOS 4.3), if I have to enter call tree options, the screen will often go dark as soon as I try to type on the keypad. Is there a setting that controls this?


Are you putting your thumb or something over the light sensor? You can’t actually see it anymore (you could on the 3G and 3Gs) - but try this:

  1. Make a phone call to a friend (or your home/office phone) so that you can test this out.
  2. Put your finger lightly over the top speaker. Did the phone go black?
  3. Test out the general location of this by starting at the far edge and moving your finger towards the center. I believe it’s right above the speaker (earpiece).

Edit: Ah, it’s actually a proximity sensor, for the purpose of shutting off the display when the phone is up against your face when you talk.

The problem is that it seems to be doing the opposite of that, or at least not picking up that I have moved it. The screen seems to go dark as I touch it. This often happens when I try to hang up.

BTW, this issue is intermittent. I was just testing it and it worked as I expected it to.


Proximity =/= movement.

How does it sense that? Radar?



IR emitter/received.
Basically, there is an LED that emits in the IR frequency. There is a detector that can tell how much IR is being received. If you have something close to it, the IR bounces back, resulting in an increased amount of IR at the received.

Some systems use specific pulses to help avoid external interference. I haven’t looked at an iPhone teardown for a while, so I’m not sure how sophisticated their solution is.

Where are they located on the unit?


Right above the earpiece, like I said in post #2. Make a phone call to someone who’ll just set the receiver down, and you can test it yourself.

Do you have a case on it? I had this problem with my Otter case. It worked fine for about a year, and gradually deteriorated. I switched the case, and it worked fine for another year. I think when those cases get scuffed up enough, they interfere with the proximity sensor.

I have no evidence beyond my experience. All I know is that changing the case fixed the problem twice.

I have an Otterbox as well. I took it apart and cleaned it yesterday. I will keep the proximity sensor in mind.

It might very well be a hardware or case problem, but you also might want to try updating to the latest version of iOS 6.