I am a bit on the older side, and can no longer hear most high pitched wrist watch alarms. My wife is always asking me what is beeping when I use the timer on my Timex watch. I can't hear it unless it is near my ear. BUT

When I backpack, I use a Suunto Core wrist watch/altimeter/etc.
I put it in my shoe near my head. It is LOUD and not too high pitched- so it will wake me up from a very sound sleep. This is the ONLY watch I have found that will be sure to wake me up.

I had a Suunto watch which came before the Core- could not hear that one. Core works well for me.