iPhone 4S Incorporates Revamped IR Sensor for Siri's 'Raise to Speak' Feature

The new iPhone 4S is the new device that offers Siri! This feature includes also a new feature called 'raise to speak'. This means that wheneverr you raise your iPhone, it senses this and together with the proximity sensor it detects your presence and where you hold it. This means the iPhone 4S' proximity sensor is always on. In comparison to the iPhone 4, on which this sensor is only active during phone calls to protect the screen from unwanted touching and to save battery power.
This feature requires a new device built in, which the guys from iFixit discovered during the teardown of the 4S and by then dindn't knew what this little black box is doing. Now it is known that this is the sensor that never sleeps and sees if you are there. This is an infra red based hardware piece.

"During our iPhone 4S teardown, iFixit buddy Markus noted that the new iPhone had a rather unusual-looking black component next to the ambient light sensor. We didn’t make much of a fuss about it since we were knee-deep in disassembly pictures, but the little black box certainly piqued our curiosity. 

Now that the teardown is wrapped up, we’ve re-opened the mystery and made a neat discovery about the 4S: that black component is an infrared LED, and the little bugger almost always wants to know if you’re nearby."

In this video iFixit shows how the sensor on an iPhone 4 is only active during a phone call and on the 4S it is active whenever the display is on:

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