I know there are a lot of smartwatches/apps which can wake you up at the best time in your sleep cycle however I'm wondering if there is one that can start a timer from the moment your movements indicate that you have fallen asleep and have gone into your sleep cycle. In other words, I'm interested in getting a smartwatch/smartwatch app that can wake me up after a certain number of hours of sleep. Sometimes I lay in bed at night and fall asleep right away. Othertimes can't fall asleep for an hour or two. If I'd like to be woken up after 6 hours of sleep say (i.e. 4 sleep cycles), is there an app which can start timing once I fall asleep and then go off when I'm in a light part of my sleep cycle say about 6 hours later. I'd really like the option to be awoken as soon as I've slept for the duration/number of sleep cycles I wanted to.