Some pilots have their own little tricks when they catch the other pilot asleep. Like setting off the fire bell, which is pretty loud, or pretending to be asleep themselves while triggering a chime or alarm that will wake the other guy up.

There once was a TWA Super Connie that overflew LAX and continued west over the pacific. The crew was finally wakened after repeated Selcal's from the ground. (It is like a doorbell saying - answer the phone).