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.

I have a set of Anker bluetooth headphones - at about $80.00, in my opinion they are about 80% as good as Bose sets costing three or more times as much.

I found a website called "A Soft Murmur" which is free to use, and generates VERY high quality 'white noise' - wind, waves, storms, etc and you can mix them. I have my own particular set of sounds, which transmit wirelessly with no issues to the headset I'm wearing to bed.

With the combination of large, soft earcups, noise cancellation, plus the whispering sussurus of that site - I don't hear any external sounds.

"It's later than you think..."