Mmmm the mandrake one wouldn't really work. They may not be able to hear it but the vibrations of the scream would still be the same and could still cause a deaf person to die of it results in hemorrhaging in the brain.
That still doesn't explain how watches work in hogworts. Technology isn't suppose to work there and watches a very complex machines that have batteries. SO HOW THE HELL DO THE STUDENTS HAVE WATCHES?!?
Fawkes headcanon, that would be cute, except Phoenix are extremely hard to catch, and choose their humans much like wands do.<<<yes we'll Newt Scamander is no ordinary wizard and he would have easily been able to find a Phoenix