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There is no sensor inside the iPhone 4. So if the headphone or dock sensor turns pink... thats it.

You're wrong. I took the backplate off my ip4 a few day ago and I saw a sensor beside the battery. There might be more but Didn't want to do an autopsy on my phone.
 
You're wrong. I took the backplate off my ip4 a few day ago and I saw a sensor beside the battery. There might be more but Didn't want to do an autopsy on my phone.

there are 2 LCI indicators near the battery area.
1 is also the warranty seal cum indicator.

Hope this helps :)
 
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