I know it might sound stupid but something that actually works is drink a lot of water few minutes before going to bed. When I do that the alarm clock always work. Make the app remind people of drinking water when it's about bed time :-)
is this so that you have to go to the bathroom in the morning so badly that you wake up naturally?
I don't feel this urge at all, I just wake up smoothly and then after 5min or so "oh I could go to the toilet, okay". I guess it's been a known trick for centuries, at least I've read somewhere it was a pretty popular strategy among indigenous folks. But hey who am I to say, I cannot even wake up with an alarm clock!