Proximity Sensors

• The proximity sensor detects the iPhone's distance from a face and turns the screen off when on a call. To accomplish this, the sensor emits an infrared beam that, when interrupted at close range by an object, signals the display to shut down. This can be tested by covering the area above the earpiece with a finger. The screen will go black until the sensor has been uncovered. This feature is commonly employed on many types of smartphones to save the user from accidental touch-screen mishaps.
  
  

Sensor Benefits

• Smartphones equipped with touch screens often provide on-screen toggles for various features. Prior to the implementation of proximity sensors, users needed to press a button to turn the screen off before taking a call. If they did not, features like hold, mute and speakerphone would seem to turn on at random. Because controls for ending a call were also on screen, accidental hang ups were very common. To combat these pitfalls, smartphone manufacturers instituted the use of proximity sensors to automatically prevent feature misfires.
  
  

Proximity Glitches

• Some iPhone 4 users suffered from software-related proximity sensor issues when the device first launched. Due to software bugs, some users experienced problems with the screen not turning off when on a call. Other users were plagued by screens that would turn off properly but then fail to turn back on once a call had ended. Some users experiencing these issues returned their iPhones in exchange for replacements only to find that the problems continued. Apple took action to resolve the issue but the fix did not come quickly.
  
  

Sensor Resolution

• A few months after the problem was first reported, Apple released a new version of the iPhone 4's operating system that contained a fix for the issue. Once downloaded and installed, iOS 4.1 resolved the proximity sensor glitch and allowed users to make and receive calls free from the irritation of accidental hang-ups. Unfortunately, the solution was so long in coming that some users gave up entirely on their iPhone 4 and went back to using older models.