Water detection
Only the iPhone 7 and iPhone 7 Plus are water-resistant, but Apple hasn't made a fully waterproof iPhone. So it's making it easier to avoid potential water damage with the iOS 10 update.
As of iOS beta 2, the software reportedly includes a warning message to unplug the lighting cable at the bottom of a device if the phone and new software detect water.
Whether or not the iPhone 7 is waterproof, as some have speculated, this iOS 10 message is a handy tool because water and a turned-on iPhone don't mix very well. Let is sit first (in rice, if you believe that myth)