Or why not do a fatigue test when you turn up for work as part of your sign on?
It would also pick up reductions in reaction time/speed of deceision making due to drugs, alcahol, stroke, stress, ....sore big toe, whatever. Each pilot does the 90 second test on the computer, it's compared to his/her history of testing and a 20% reduction from the norm shows as a fail.
Why not?