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Your iPhone or iPad will notify you of possible liquid failures. The new iOS 10 update will alert users when their device has gotten wet and is therefore also out of warranty.
Apple devices already have indicators that change depending on whether our phone gets wet, something that will help us know if it has gotten wet and if we have lost the warranty. But also now iOS 10 will alert us in the operating system itself.
Specifically, a warning will tell us to disconnect a Lightning cable if it detects that it is wet, an alert that if we ignore we could see how is our iPhone damaged.
Since iOS 10 beta 3 you can see this notice that unfortunately some Reddit users have experienced when connecting a wet cable.

How to know if the iPhone has gotten wet
In any case, the new notice by software, which will arrive with iOS 10 is not the only indicator. Apple incorporates into all its iPhone phones and iPod devices a physical indicator that changes color when wet.
This indicator helps us to know if the device has come into contact with liquids, so it could have a fault as a result. Also, we would already know that Apple would not cover failures under warranty.

In any case, Apple recommends that we contact the official authorized service if we find said indicator red in color, since it could also fail.
But as we say, soon iOS 10 will alert us by software without having to look at these indicators.