The Nike+ Sensor: Run tracking made easy The Nike+ Sensor makes it easy to track your time, distance, pace & more while you run. When your training is finish, upload your run data to Nikeplus.com, worlds largest running club, where you can monitor your progress, join challenges, map your runs & connect with friends. The sensor is sold individually, so its ideal if youre due for a replacement, want another one for a second pair of Nike+ ready shoes or need one to hook up to your Apple device. How it Works Simply place the Nike+ Sensor under the sockliner of your left Nike+ ready shoe & start running to sync it with your Nike+ Sport Watch GPS, iPhone 3GS or other Nike+ tracking device. The sensor measures your pace, distance, time elapsed & calories burned. This information is transmitted wirelessly to your Nike+ tracking device for real-time feedback while you train.