so this could be a project that might be worth doing: using the iphone's sensor's to track your running/walking.
there is a sample app called "AccelerometerGraph" on apple's site: https://developer.apple.com/iphone/library/samplecode/AccelerometerGraph/index.html
there is a sample app called "AccelerometerGraph" on apple's site: https://developer.apple.com/iphone/library/samplecode/AccelerometerGraph/index.html
Description
AccelerometerGraph sample application graphs the motion of the device along each of three axes. It demonstrates how to use the UIAccelerometer class as well as how to render Quartz 2D graphics in a UIView that continually updates. It also demonstrates a technique to "remove" the gravity influence from the accelerometer values using a basic high-pass filter.