Did you know that the iPhone has a proximity sensor?

In a recent interview with Alasdair Allan regarding the iPhone sensor suite, he shared some information about a little known sensor.The proximity sensor is an infrared diode.

I think it's actually now a pair of infrared diodes in the iPhone 3G. And it's the reason why when you put your iPhone to your head, the screen goes blank. It basically just uses this infrared LED near the earpiece to detect reflections from large objects, like your head. If you actually take a picture of the iPhone when it's in call mode, with a normal web cam, you'd actually be able to see right next to the earpiece a sort of glowing red dot which is the proximity sensor. Because, of course, web cam CCDs are sensitive in the infrared so it would actually show up. This was a bit of a scandal early on in the iPhone's life. The original Google Search app used undocumented SDK call to use this, so you could actually speak into the speech search so Apple, and everyone really was very annoyed about this. They actually enabled it for everyone in the 3.0 SDK.