Apple staff will use flashlights to illuminate the headphone slot and data cable interface. The earphone slot and the data cable interface have water inlet test paper, which can be used to detect whether the mobile phone has water. However, these papers are usually difficult to find because they are posted in some inconspicuous positions.

Water inlet test paper at data port position

Headphone jack water inlet test paper

How to judge whether there is water through these papers? It's actually quite simple. These test strips are white and turn red when they come into contact with water, so Apple staff can know what color the test strips are with flashlights. Of course, we can also use this method to check whether the purchased second-hand iPhone is flooded.

In addition to the outside of the fuselage, there are also these test papers inside the fuselage. The red circle below is the water inlet test paper inside the fuselage. This test paper was originally all white. Now I see that the right side of the test paper turns red because it has been tested with water drops before, and the part of the test paper stained with water will turn red immediately.

However, it is often explained that the mobile phone did not fall into the water, but why the water test paper turned red. In fact, these absorbent test papers will not only turn red when they meet water, but also turn red when the humidity is particularly high, such as bringing iPhone into the bathroom.