Two Iphones in our house and neither have been tripped. I live in a humid environment and have not had a problem. I have also had a phone replaced due to cracks. Apple has also repaired my Macbook due to stress cracks and repaired my wife's MBA with a broken hinge no questions asked. Yeah, their customer service really sucks.... 
I've played with the sensors in question on an older piece of equipment and can say that the only way I was able to trip it was to drop water on it. Misting and breathing did not work... That being said, if you work out and sweat I recommend using an cheaper Ipod for the task as it can run down your cord and works it way into the jack.
I've played with the sensors in question on an older piece of equipment and can say that the only way I was able to trip it was to drop water on it. Misting and breathing did not work... That being said, if you work out and sweat I recommend using an cheaper Ipod for the task as it can run down your cord and works it way into the jack.