Madeleine Pulver, 18, was freed unhurt from the device late on Wednesday by bomb squad specialists. Police later said there had been no explosive, but confirmed that there was a note making demands.
Detective Superintendent Luke Moore, of New South Wales police, would not reveal the note's contents, but said: "We are treating this as an attempted extortion, a very serious attempted extortion."
As police launched a manhunt for a masked man said to have broken in to the family home, Pulver's father, Bill, fought back tears as he talked about his daughter's horrifying ordeal.
"We as parents are extraordinarily proud of Maddy," he said, his wife , Belinda Pulver, at his side. "I think she has woken up this morning in pretty good spirits. She's a little tired, a little sore, from holding this damned device in place for about 10 hours."