Sensor on back opposite of camera?

[idunk]

I'm not sure if this has been posted in another thread but i looked in the main sticky and didn't see anything on it.
I was shining a flashlight on the plastic back of my 3GS and on the opposite side of the camera i noticed something that looks like the sensor holes on the front.
Does anybody know what this might be for?

 

[TheNewsPaperBoy]

There is nothing there, just plastic.

 

[bruinsrme]

sensors on the front are for light levels for auto brightness

 

[aprofetto]

Hmm... I remember seeing a post when the 3G came out, something about a chip or sensor being visible through the black plastic with a black light or something...

Can anyone confirm this?

 

[tsvb]

There are three sensors on the top left hand side of the 3G. I assume one is the ambient light sensor and one is the proximity sensor but I am not sure what the other is.

 

[mac2thefuture]

In certain natural light conditions I too have seen 3 slightly purple circles on the front opposite the camera, in an 'L' shape if you will.

 

[iMacDragon]

I believe underneath that IR readable hole is the serial number 2d tag, for factory purposes.

 

[lemonademaker]

I was kind of wondering why my Otterbox defender had that xtra window to the left of the earphone where the "L" shape would be.... now i know....

 

[BNZ1]

In certain natural light conditions I too have seen 3 slightly purple circles on the front opposite the camera, in an 'L' shape if you will.

IR Light (not on first gen), Proximity Sensor (uses IR light on 3G and 3GS, ambient light on first gen) and the auto brightness sensor.

If you want proof hold the phone up to a video camera whilst on a call and watch the IR Led strobe as it puts out light for the proximity sensor.

 

[aprofetto]

...

If you want proof hold the phone up to a video camera whilst on a call and watch the IR Led strobe as it puts out light for the proximity sensor.

I've seen this in action once while on a call in the darkness of my backyard. Kind of cool.