We all know that cell phone manufacturers love to use the old “you dropped your phone in water” excuse for not fixing your phone. They usually make it pretty easy to turn you away because they have a little white sticker that changes color when it comes into contact with water. These are usually stuck somewhere easy to see, like behind the battery. However, where would you find one of these on an iPhone?
It's quite obvious that the iPhone doesn't have the little sticker because it's not shown up in any of the tear downs that we've seen. Or has it? If you know where to look, you can find this magic sticker on any iPhone (or iPod Touch for that matter).
Look at the top of your iPhone, where the headphone jack is. Now peer down the jack and you'll see the sensor. Now pour a little water on that (actually, don't do that) and it will change color. Now all an Apple employee has to do is take one look at it and they'll know you went swimming with your precious iPhone in your pocket.
A Water Sensor in iPhone and iPod Touch!? [via hardmac]