iPhone screen remains active during calls

Q: I have an iPhone 4 and when I make calls I find that as I have my face against the screen I end up making other calls and cutting people off and many other things I do not want to happen as I cannot see how you can guard the screen against unwanted actions. Can anyone tell me how to activate a key guard or something as I have tried everything including the iPhone manual! Thank you.

– Katherine

A: The iPhone has a proximity sensor that should turn the screen off and disable touch input entirely when you are holding it up against your head.

This sensor is hidden behind the glass near the earpiece and should normally activate during a phone call when any object is within about an inch or two of the earpiece area. This feature is designed specifically to prevent the problem that you are encountering.

Note that you should avoid placing anything over the screen near the earpiece, such as a wrap-around case or highly opaque screen films as these can affect the reliability of the proximity sensor.

Also, some iPhone 4 units unfortunately had a problem where the proximity sensor wasn’t activating consistently. This issue was supposed to be resolved in the iOS 4.1 update released last week, so if you are still running iOS 4.0 on your iPhone you should connect to iTunes and update to the latest version to see if this fixes the problem.

If you are running iOS 4.1 and are still having this issue even on an uncovered screen, this may indicate a hardware problem with the proximity sensor and you should look into getting the iPhone serviced.