May 15, 2008
A lot of the magic of the iPhone is that things just work. Intuitively. A great example is during a call — when you bring the phone to your ear, the touch screen and display shut off automatically, to keep you from hanging up or dialing with your face. When you pull it away, the screen lights back up and the touch screen is activated again. All automagically.
Of course, that auto-magic has some real technology behind it — there is a little proximity sensor that both emits and detects an infrared beam — during a call, when an object (such as your ear) comes near it (within an inch or so), it reflects the beam back to the detector and shuts down the screen. When the reflection stops, the screen comes back on.
The proximity sensor is hidden under the glass just above the speaker hole — the overly-contrasty image above shows the rough location. You can see the actual sensor on this disassembly photo from iFixit.
Amazingly, nearly a year after the introduction of the iPhone, there are still a lot of cases being sold (even in places you think would know better) that cover up the proximity sensor with opaque material. Put one of these on your iPhone, and you too can dial with your face, hang up with your cheek, and get frustrated by not being able to punch in digits during a call.
Worse, there are more than a few rumors out there that if you leave the proximity sensor covered long enough, it can “stick” and just fail to work altogether — even if you take the cover off. If it sticks in the “screen off” position, you’re done until you get your phone repaired.
The moral of the story is be careful of your iPhone case — if you try a new case, double-check that the proximity sensor still works as it should, and if not, take it back and get a different one.
If you’ve found a great case that does work properly — or have a case horror story — share it with us in the comments!