As the hours ticked by and cold set in, Maddie never lost her poise

Madeleine Pulver, 18 years old and alone at home preparing for her HSC trial exams, reported that a man in a balaclava had entered her family's house and forced her to sit in the kitchen while he locked a bomb around her neck.

According to some reports, she was told by the intruder that if she moved she would die, and if she told police too much, he would know.

The intruder, she understood, could remotely detonate the bomb at her throat.

The man attached a note outlining his demands - thought not to be monetary - as well as a USB flash drive and fled.

A single police car with a crew of two was dispatched from Mosman police station. Any reservations authorities may have held about the seriousness of the situation were quickly swept away.

It is not known whether both officers initially entered the Pulver home. What is known is that as soon as it became clear a young woman had a bomb locked around her neck, Constable Karen Lowden volunteered to risk her life to stay with her.

''She was not wearing any protective clothing or equipment, she wasn't trained as a negotiator, but she made the decision herself, this young officer, to stay with Madeleine and make sure she tried to remain calm and she wasn't left alone, provided moral support for her, and she did an outstanding job in that regard," Assistant Police Commissioner Mark Murdoch said later.

Outside, Constable Lowden's partner went into action. The emergency services response was immediate and vast.

''We saw a mass of police screaming down the road and coming in,'' said a neighbour who was farewelling lunch guests at her front door sometime between 2.30pm and 3pm. ''Police Rescue and fire engines, and policemen on motorbikes. Just masses of police.'' Soon those police were joined by NSW Fire Brigades and State Emergency Services. Helicopters thundered overhead.

Outside the Pulver home - an architect's vision in glass and concrete, brick and sandstone - a woman was seen bent double and sobbing.

But inside, Madeleine - Maddie to her friends at Wenona girls school - and Constable Lowden sat still and talked.

The pair waited two hours while bomb disposal technicians made painstaking preparations to enter the home and begin work on the device.

The technicians contacted the Australian Federal Police and Australian Defence Force to get information from the Australian Bomb Data Centre.

It would have been of little comfort to the two young women to know that collar-bombs typically carry only a small explosive charge as they sit so close to vital organs.

Only after two bomb technicians and two police negotiators were in place in the kitchen, did the young officer leave Maddie's side at about 5.40pm. Madeleine would not be freed for another six hours.

By early evening all of Sydney knew something about what was going on inside the Pulvers' home. Neighbours and friends of Maddie milled around the police cordon at the corner of Thompson Street and Burrawong Avenue.

The incongruity of it all was shocking. As an unseasonably warm winter dusk approached on a wealthy street in view of Sydney Harbour, men in armoured Hurt Locker suits unloaded a bomb disposal robot and a portable X-ray.

Before dawn broke in Sydney, Maddie had been described in the British press as an heiress and her well-to-do family elevated to one of Australia's richest. The crime was so odd, so out of character in this city of rich criminal history, that rumour and speculation ran hot. During a police press conference yesterday the Commander of the Robbery and Serious Crime Squad, Detective Superintendent Luke Moore, was moved to remind reporters who had asked if Madeleine was a person of interest that the girl was a victim.

By nightfall Maddie's arms were aching from holding the shoebox-sized bomb in place. With the power cut the house grew cold and Maddie was wrapped in blankets.

The cold was a problem.

Roy Ramm, a former commander of specialist operations with Scotland Yard's hostage response team, said police who went to Maddie's aid would have faced an extremely complex and stressful situation, including the prospect of the device being remotely detonated, or set off by a ''trembler switch'', a device that triggers a bomb when it is tilted beyond a certain angle. ''They primarily would have been concerned about keeping this young woman calm … to sit extremely still,'' he told ABC Radio.

Though the evening was relatively warm, Maddie's stillness and stress had accentuated her sense of cold.

Sandy McFarlane, the head of the Centre for Military and Veterans' Health at the University of Adelaide, said people went into a sort of ''sympathetic overdrive'' during intense stress, and often complained of significant cold.

''Accident victims who have been badly injured will often start shivering and feeling cold,'' he said. ''The body goes into alarm mode.''

Police said the popular schoolgirl's poise throughout the ordeal was remarkable. Outside, her parents were doing it tough. Finally, a few minutes before midnight, police managed to remove the device from Madeleine's neck. She was reunited with her parents and rushed to Royal North Shore Hospital.

Only after they removed the device were police able to ascertain that the collar-bomb was ''a very elaborate, very sophisticated'' hoax, a device designed to look like a bomb but one that contained no explosive material.

At dawn and through the day yesterday Burrawong Avenue remained blocked off around the Pulver's house. Forensic detectives worked over the house while others concentrated on the device itself. Still more appeared to be taking apart computers in Mr Pulver's home office.

Yesterday afternoon Maddie's parents held a press conference to thank all those who had worked to free Maddie, and to care for her as she sat in her kitchen with a bomb at her throat.

''They were an incredible comfort during a horrific ordeal,'' Mr Pulver said.

Maddie, he said, was coping well. ''She is a little tired, a little sore from holding this damned device in place for about 10 hours.''

with staff reporters