The short answer:

The iPhone has a motion sensor, and we use that to count your steps.  The sensor is the same type as is in the high-end pedometer devices, and the accuracy of StepTrakLite is about the same or a little better than the best New Lifestyles or Omron pedometer you can buy in the store.

The longer answer, which is a little more geeky:

The iPhone includes a three-axis accelerometer — a type of motion sensor that is used in the iPhone primarily to do landscape-to-portrait display orientation changes, but which is used in high-end pedometers, the Nintendo Wii motion controler, and numerous other applications involving motion sensing.

It turns out that different types of activities have different motion signatures.  Using techniques analogous to speech recognition, StepTrakLight analyzes the motion of the phone (as measured by the accelerometer) and figures out what sort of activity you are engaging in.  It also knows just what a step “looks” like, and can count them very accurately.

So, if you start STL and take a few steps, each time you step your body moves in a distinctive way, and the software recognizes that and adds one to a counter.   Likewise we can tell the difference between walking, running, and other types of activities as well.

Hope this helps.

    Rich

Previously, StepTrakLite was available only on the iPhone and in the US AppStore.

The first major update to StepTrakLite is now in review by Apple.  It includes buit-in Twitter support for posting step Tweets directly to your Twitter timeline, making it easy to record and share your exercise.

StepTrakLite now has a Support Community to connect users and developers.

    Cheers,

    Rich