Who Watches The Watch?

(My dad and I have just gotten into the car to go somewhere. Note that my dad typically wears his watch on his left wrist, and today is no exception.)

Dad: *glancing at his right wrist* “Now, I don’t have my watch, so…”

Me: *looking at his other wrist* “What do you mean?”

Dad: *looks at his watch, then knocks on his forehead* “Hello, anybody home?”