I like to use my iPod Touch to put me to sleep at night by playing soothing music. The device will keep playing music all night though, sapping battery power. Fortunately, you can set your iPhone, iPad or iPod Touch to automatically sleep after a certain amount of time using the Clock app.
1. From the Home menu, select Clock.
2. Select Timer.
3. Set the number of hours and minutes, then tap When Timer Ends.
4. Scroll all the way to the bottom and choose Sleep iPhone, iPad or iPod.
5. Tap Set in the upper-right corner.
6. Tap Start to start the timer.
Now the iPhone, iPad or iPod Touch will automatically sleep after the time interval you set.