Spire tracks the significant activity of your body and your mind. More specifically, Spire tracks physical activity like walking and running as well as periods of time that reflect a mind that is Calm, Tense, or Focused. It tracks your state of mind by sensing patterns in how you breathe.
Of course, with any sensor, there can be 'noise' in the signal and part of Spire's job is to be able to tell the noise from the signal. This is something that is constantly being improved. It's actually a rather complex problem if you consider the amount of diversity in the human body between genders, body types, ages, weights, and then add clothing to that: shorts, pants, slacks, skirts, and the like. But that's our job, and we love making Spire more and more useful to you.