Some great ideas here!
Maybe the cabin crew could wear 'snore detectors' then they could be alerted if the pilots fall asleep?
Or maybe have a 'view the flight deck' as an option on the in flight entertainment then any passenger could alert the cabin crew if they see anything untoward happening in the cockpit.
I like the one about cabin crew fitted with radios tuned to 121.5.
Tracy this is London, could you check the crew are okay?
London this is Tracy
Is that Tracy on the XXX123
Mayd....
No this is Tracy on the CCC123
Sorry Tracy
Mayd....
Hi London this is Tracy on XXX123 what's the problem
No problem, I'm calling Tracy CCC123
Mayd...
Okay
Did someone call Tracy DDD123
Mayd...
No Tracy XXX123
Oh okay
Was that a Mayday I heard.
I don't know
Who said that?