All iPhone models come equipped with a few moisture indicators which change colors when exposed to liquid. The purpose of these indicators is to let Apple know if your iPhone was potentially damaged because it fell in the bathtub or was otherwise exposed to moisture. This is important, because moisture exposure voids the manufacturer's warranty that comes with all iPhone models. If you are concerned your phone may have been exposed to moisture, checking the color of the indicators is a good way to know for sure.
Locate the moisture indicators on your iPhone. If you have a first-generation iPhone, you will find only one moisture indicator, which is located inside the headphone jack. All other iPhone models have moisture indicators in both the headphone jack and inside the dock connector on the bottom of the phone.
Shine a light into the headphone jack and the dock connector to find the moisture indicator. At the bottom of your iPhone's headphone jack, you will see a small circle that is either silver or a reddish-pink color. The indicator in the dock connector is a small rectangle near the center of the port. It will also be either silver or reddish-pink in color.
Determine if your iPhone's moisture indicators were activated. If your iPhone was exposed to moisture, the indicator will appear as either a full or partial dot that is reddish-pink in color. Under normal conditions, the moisture indicator will appear silver.