Apple MA368LL/B Nike + iPod Wireless Sensor to Track Your Workouts.

This Apple 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. 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.