New South Wales state Police Assistant Commissioner Mark Murdoch would not comment, however, on reports the device had been strapped to her by someone she did not know.
“There's a device in the house in the vicinity of the young woman. That device is still being examined as we speak,” he told reporters. “We are treating the device as live until we know otherwise.”
Police said they were called to the house in the wealthy suburb of Mosman by an 18-year-old woman around 2:30 p.m. They said the case was “not being treated as self-harm.”
“There are operational reasons for playing our cards pretty close to our chest,” Mr. Murdoch said. “The young lady is fine and doing her best to assist the police to find out exactly what's gone on,” Mr. Murdoch said.
He appealed for members of the public to call police with any information of suspicious activity around the house earlier Wednesday.
Surrounding homes were evacuated, several streets were closed to traffic and medical and fire crews were on standby.
Mr. Murdoch said the woman's parents were with police outside the house and were being updated on the situation.