A man who has guarded two New Zealand prime ministers has created an app which he hopes will lower the danger posed by stalkers.
The app was inspired by Christie Marceau's death and has been bought by people in seven countries.
Darren Morton, with business partner and former British police detective Keith Suddes, provide security-related risk management services with their company Patronus International.
In December, they introduced their smartphone app Stalker Awareness to give people information on how to manage and survive "a wide range of personal safety situations".
It also teaches people how to identify danger and includes GPS mapping for the nearest police station. It can be used anywhere in the world.
Mr Morton said they wanted to create something which gave people access to information to help them from becoming a victim.
The pair developed the idea after Ms Marceau, 18, was fatally stabbed in her North Shore home in 2011.
"What happens in a time of high stress or [in] a life-threatening situation, you find motor skills go, your memory goes and your ability to quite often make sound decisions is alsoaffected.
"So what we've done is put all of that information on to something that people can have on their phone."
The $1.20 app derives from the security firm's Stalking Awareness programme. Mr Morton said this provided training that not only gave an insight into stalkers' mindset, but also instructed in preventive and response safety measures for anyone being stalked.
"If we can prevent one victim, that's what it's all about."
Stalking hit the news lately when Shortland Street star Teuila Blakely needed a security guard because a man was allegedly stalking her.
Mr Morton joined the police in 1985 and was a detective for nine years and a member of the police VIP protection squad for three years.
During that time, he was involved in the protection of two prime ministers - though he wouldn't say who - foreign heads of state and the royal family.
He formed Patronus International with Mr Suddes last July.
The company shares its name with a protection spell in the Harry Potter books, but Mr Morton said that's not where the name came from, it was just an unfortunate coincidence.
He came up with it after searching ancient words for protection.
"Had I known Harry Potter had it, I would have named it something different," Mr Morton said.
Patronus International has also created apps for teens, robbery, travel and home safety among others.
He said a lot of the information available online about such issues was "from people who have been in the industry five minutes and consider themselves an expert".