Prepare for a multi-part answer! :)

So... I rarely fall asleep with them on. Usually, I seem to sense when I'm really falling asleep for real, and peel them off.

About 95% of the time, my eyes "flap" open 30-60 mins ahead of my intended wake-up time. Alarm is almost superfluous, BUT I use a count-down timer which has a pretty piercing beep which I can easily hear in the rare event I still have the headphones on.

I'm also fortunate enough to not have a regular job - I'm a freelance IT tech, so I can schedule my first appointments for 10:00am, which gives me 5+ hrs after my intended wake up time of 5:00am. Also - the vast majority of my clients are pretty laid-back and would be understanding if I accidentally oversleep and run late - but that hasn't even happened yet.