Sleep Cycle is a fantastic app for keeping track of your sleeping patterns and waking you when you are in the lightest sleep phase. The app allows you to choose a latest wake up time and then wakes you a maximum of 30 minutes before this time but when you are in the lightest sleep phase. It cleverly uses the accelerometer to monitor movement and determine your sleep phase. Waking up in the lightest sleep phase has left me feeling much fresher, better rested and more relaxed - couldn't live without it!