The iPhone 3GS, like the second generation iPod Touch, includes built-in Nike + iPod support to monitor your workouts. Runners can purchase the Nike + iPod Sensor for $19 and slip it into either a Nike+ compatible shoe or any shoe (using one of the below hacks). The iPhone 3GS is thus capable of tracking distance, calories, pace, and workout duration during a run. The iPhone 3GS has a built-in receiver that eliminates the need to plug in the receiver sold with the Nike + iPod Sport Kit.
Using the Nike + iPod app
The Nike + iPod app is easy to use after you link it to your iPhone 3GS. You simply go to Settings, choose Nike + iPod, and turn Nike + iPod on. When Nike + iPod is turned on, its icon appears in Springboard (iPhone desktop). The app provides audible feedback on your speed, distance, time elapsed, and calories burned during a running (or walking) workout.
Note:If you have more than 176 apps installed--passing the display limit of Springboard--and you are running iPhone OS 3.0, you'll have to use Spotlight to launch the Nike+ app.
Once you have completed your run (or walk), dock your iPhone to your computer and use iTunes (Apple support document) to upload your workout statistics to NikePlus.com. You use that Web site to track your progress, set your goals, and participate in challenges against others.
Hack your own shoe
If you happen to like other brands of shoes, you can learn from others who have discovered ways to make the Nike+ sensor work with their favorite pairs of shoes. See some do-it-yourself examples at Instructables.com and Gadgetpage.com, or buy yourself a Shoe Pouch if you are lazy. Spendthrifts will appreciate this YouTube video for a real cheap sensor and shoe hack:
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