You’ll never realize how important it is to have a water-resistant smartphone on you until you have to use one to call for help while you’re treading water. That’s what happened to a group of friends visiting Japan recently after their boat capsized in rough seas. A water-resistant iPhone allowed them to call the local emergency number and have the coast guard save them.

Rachel Neal and her friends were visiting an island off the coast of Okinawa when they were forced to abandon the ship. She explained on The Today Show that she always has a “go bag” ready at all times, and the iPhones belonging to her and her friends were in it. After jumping overboard, they tried to use the phones to call for help. One was already water damaged, but Neal’s iPhone was still working, as it’s a water-resistant device.

As the coast guard came to the rescue, the group used the same smartphone to record footage of their friends being pulled out of the water. It’s unclear what device she used, but all iPhone models starting with the iPhone 7 are water-resistant, which means that any of the new phones would have worked.

The story was featured on The Today Show (see video above), but only after Neal wrote a note to the company thanking them for making a quality product. Apple CEO Tim Cook, who rarely uses Twitter, retweeted the story:

The Apple Watch has traditional been the life-saving Apple-made device, after detecting health condition that the user wasn’t aware of. That’s because the Apple Watch features sensors that monitor your heart rate and it can also tell if you’ve fallen. This time around it was a smartphone feature most of us take for granted.

Hopefully, you’ll never have to test your iPhone or Android device in such conditions, but if you’re out in the water often, it might be a good idea to check if your device is water-resistant. Also, it’s a good idea to learn the local emergency numbers when traveling abroad. It might save your life.