The WakeMate, a sensor-laden wristband packaged with sleep analysis software, determines the optimal wake-up point in your REM cycle and adjusts your alarm for that moment. It also lets you say you really use your iPhone 24/7.

From the product page:
Problem: Traditional alarm clocks wake you at a random point in your sleep cycle, leaving you feeling groggy.
Solution: The WakeMate will analyze your sleep to find the optimal time for you to wake up. You will feel refreshed and energized every time you wake, even from naps!
Problem: After sleeping, you may still feel tired – you’re getting poor quality sleep without realizing why.
Solution: View a full analysis of your sleep on our Analytics Platform. You will receive personalized instructions on how to improve your sleep so you can have your best night’s sleep, every night.

More info & purchase: link