I've tried services likes this before but it's too easy to know what it is and ignore it and then fall back asleep. Maybe I'm just more stubborn than everyone else.
I'm much more tempted to write something for a Raspberry Pi with speakers attached that will immediately begin yelling at me at the proper time. More configurable, and less prone to weird phone-related issues. (The only vulnerability would be if I started unplugging the device or speakers in my sleep, but there are ways to mitigate that.)