I do trust my body. Its not that I am getting signals from my body to go up for air. its just that sometimes I am just not sure how long I have been under. The watch is to make sure I dont stay down longer than I should. When Im in shape I can hold my breath for 4 minutes. 3:30 under water. Sometimes time can fly by really fast. And sometimes time can go by very slow. Trust me if I feel the need to breath or that something is not right I go up for air.