Afaik train drivers have to push a certain button in certain time intervals to
make sure they are not asleep and if they stopp pushing it the train will
automatically brake and come to a stop.
Doesn't something similiar exist
in airplane cockpits? Having an alarm sound going off to wake the pilots if they
stop showing activity after a certain time period?
And what? Put on the brakes and land the plane?
Pilots are in the air for pretty low maximum hours compared to bus,train and coach drivers. The least I would expect is they could be conscious. Power naps are for on the ground, in bed and after the CC...