iphone proximity sensor problem and fix

As soon as Apple launched it's attractive, powerful and consequently market-dominating smart phone iPhone4, there are also many complaints about its performance. Besides antenna issues, malfunctions caused by its proximity sensor are also of the hot topics among its users.
Mac World gives a  good summary of this problem, in its article "Answers to your iPhone 4 questions: The proximity issue".
Below is a summary.

Purpose: detect when iPhone is close to one's face (cheek), supposedly for making (or during) a phone call
Action: turn off the display and disable touch sensing functions, avoid unintentional operations and reduce power consumption

However like any other "intelligent" devices/features, it does not always work perfectly (aka as one expected). According to Wikipedia, "A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.". Among the recognized methods, iPhone uses infrared sensor (at least two inside the ear speaker). Although only for iPhone 3G, Mac World's "How the iPhone works" gives a great summary of the "sciences" behind an iPhone, including proximity sensing. In fact it also have a light sensor on the top-left corner, above the screen. The later is used for automatically adjust the brightness of the LED light, according to ambient light.
Anyway, back to the imperfect performance of iPhone. Since it is in effect only sensing ambient changes in infrared light, iPhone will work the same way not only by the proximity of ear/cheek, but also any other type of changes than consequently cause the same amount of changes in infrared light.
In one word, an iPhone does not really "knows" that an ear is getting close or pressing against it, for sure.

On the other hand, since this feature of iPhone does more good than harm, most of the users do just simply get rid of it, but try to find ways to work around. In fact, only a small percentage of users have had malfunction experiences caused by proximity sensor. And it does not take a rocket scientist to resolved the problem: Settings reset or a hard reboot will do the trick.

For those who do not even know that the problem here is, Youtube posts as below gives a very good description.


Some more tips about sensors in smart phone here. In fact, the other mobile phone platform Android also has similar sensing features as below. The left side is the system variables for developers.

TYPE_ACCELEROMETER	Acceleration sensor
TYPE_GYROSCOPE	Gyroscope(orientation sensor)
TYPE_LIGHT	light sensor(aka Photodetector)
TYPE_MAGNETIC_FIELD	magnetic sensor(aka Magnetometer)
TYPE_ORIENTATION	Orientation sensor
TYPE_PRESSURE	Pressure sensor
TYPE_PROXIMITY	Proximity sensor
TYPE_TEMPERATURE	temperature sensor(aka Thermometer)

What is more, although hardly categorized as sensor, there is also GPS receiver, which can "sense" the whereabouts of a mobile device, if enough signal from Satellites can be received.