An Australian man has made the ultimate high-tech marriage proposal, treating his girlfriend to an 11-hour treasure hunt using a custom-built iPhone app he designed himself.

Sydney man Sahba Idelkhani, a computer security engineer, decided to combine his girlfriend's love of adventure games with his own "geeky" interests to create the iPhone app that took three months to build at a cost of $1500.

The iPhone is a popular theme among gadget-loving romantics, and last month a US man popped the question with a mock Apple iPhone TV ad he created to play on the big screen for his girlfriend, causing an immediate internet sensation.

The iPhone app: took the couple on a journey through memory lane.

Idelkhani's proposal was no less public. His app took the form of a game app with a number of levels, and his girlfriend, Melody, was directed to travel a 200km circuit of special locations to complete the game - as photos and location data were sent via the app to a Facebook page for family and friends to follow.

"All of the locations had some meaning behind them. For instance, Melody loves Masterchef and Adriano Zumbo - so went to his café and had breakfast there. There were a number of other places like a park in the city where we used to go to quite often," said Idelkhani.

As Melody reached each destination, she would move up a level, and receive new instructions on where to go and which items to collect.

Facebook updates of the proposal: sent via iPhone.

After several hours on the road, the game finally culminated in a romantic dinner for two - and Melody was then instructed to go upstairs to the penthouse suite where she had to locate a card which was sewn into one of her teddy bears. On it was written: "Will you marry me".

"She cried a fair bit," said Idelkhani, explaining that the card carrying the proposal had been sewn into the bear a full three years earlier when he first had the toy made, and long before he had concocted the final game plan.

"I was really surprised it had been in there for three years," said Melody, who confessed she was a fan of adventure reality TV shows like the Amazing Race.

"It was definitely my sort of thing. At first it was a novelty but at the end when we went to the penthouse and had our dinner it was really romantic," she said.

The couple plan to wed in February and are having an outdoor ceremony on a private property.