"You trust people. Your whole house is open for view and then to realise something so special was gone - I was feeling sick to my stomach."

A platinum diamond engagement ring worth almost $30,000 was stolen from an Auckland open home.

Melissa Copestake says she was devastated when she realised the precious ring was missing from her Birkenhead home after it had been opened to prospective buyers on a Saturday in October.

She said she always wears the ring when she goes out, but when at home often takes it off and puts it away.

An Emerald cut diamond ring similar to the one Melissa Copestake lost.

"It was tucked away in a small pouch at the back of a wardrobe with two other pieces of jewellery that I always wear. I was cleaning the house for the open home and looking after my toddler so I took off my jewellery and put it away," she said.

She regrets leaving the small cloth pouch in the wardrobe while the family left the Harcourts real estate agent to show people around. It was the last open home the day before the auction of their property.

"It wasn't until the next day just before the auction that I realised it was missing. I went to put it on for the auction, because I always feel good when I wear it and I saw that it was gone. My heart just sank," she said.

LIZ MCDONALD/FAIRFAX NZ Harcourts says it takes all prospective buyers details before letting them in to Open Homes.

Strangely, the other two pieces of jewellery were still in the pouch.

"While the auction was going on, we were just rifling through everything trying to find the ring. It was too high for my toddler to reach but I just questioned whether I had snagged it on something or dropped it somehow," she said.

When it didn't show up, they alerted the real estate company and the police.

"You trust people. Your whole house is open for view and then to realise something so special, my engagement ring, was gone. I was feeling sick to my stomach," she said.

She rang her insurance company, and was initially told her original policy had an exclusion for open homes and the ring would not be covered.

However, luckily the company honoured a new policy which did cover the theft.

When the insurance company rang a valuer, the valuer alerted them to a woman who had brought in an identical ring that day.

Police were able to match up the CCTV footage of the woman who visited the valuer with the list of names and numbers the real estate agency had compiled from people at the open home.

The woman had provided her real name and address before going into the open home.

Police executed a search warrant and retrieved the ring for a very relieved Copestake.

Copestake said the platinum emerald cut diamond ring was expensive but she could not put a price on the sentimental value.

"We were living in Melbourne and I saw the ring in a shop window, I joked to Chester "that's my ring" but there was no way we could justify spending that much money," she said.

Nine months later, Chester proposed to Melissa with the ring of her dreams.

"He squirrelled away, but he didn't spend close to $30,000 on it."

The couple got married five years ago and then moved back to New Zealand from Melbourne. They are moving house again to live closer to Copestake's parents.

Her message to other vendors is to take all valuables out of the house before an open home.

Harcourts NZ chief executive Hayden Duncan said the company always advised anybody having an open home to make sure valuable items were kept secure.

"We take the security of our clients very seriously. We take the names and phone numbers of everybody that comes through open homes. If people don't want to leave their names we don't let them in.

And we're pleased that in this case, with those systems in place and by assisting the police with their enquiry there was a happy ending and the property was recovered."

A woman has appeared in the North Shore District Court charged with stealing the ring valued at $29,950.