This wireless sensor works with your iPod nano or iPod touch (2nd generation) to track your workouts. Insert it into the built-in pocket beneath the insole of your Nike+ shoe and pair it with your existing Nike + iPod receiver attached to your iPod nano. This sensor is perfect as a replacement for a sensor that has been lost or has exhausted its battery. Or it's great if you want to have a sensor for a second pair of Nike+ shoes. If you have an iPod touch (2nd generation), all you need to track your workouts is this wireless sensor. With its built-in support for Nike + iPod, your iPod touch (2nd generation) can deliver all the benefits of the Nike + iPod Sport Kit without the extra receiver. Please note: This package includes only the Nike + iPod wireless sensor. If you also need the wireless receiver for iPod nano, purchase the complete Nike + iPod Sport Kit.