I have been using my iPhone 4 in an armband for the gym for about a year and a half, and never had any problems. So I have bought an armband for the gym on ebay for my iPhone 5, its pretty soft so I am not really worried about it scratching. However, there is quite a large open port on the bottom where the dock connector, speaker, microphone is. I was concerned that if a small amount of sweat got into that area triggered the water sensor, it would void the warranty. Does anybody know where the water sensor is located on the iPhone 5?