Depending on your iPod nano generation, the way how to turn your device into sleep mode may be different. If you have the latest iPod nano with a touch screen without a click wheel on the front, the Sleep/Wake button is located on the top of your device. Press and hold this button until the screen goes dark. Your iPod is now in sleep mode.
To turn your iPod nano (older) with a click wheel on the front into sleep mode, press and hold the Play/Pause button on the front until the screen goes dark. Your iPod is now in sleep mode.
When you’re ready to turn your iPod back on, and you don’t know how to do so visit this article: