Lost in the bush? Just use your mobile phone to call the rescue helicopter flying above

Rescuers will soon have the ability to talk to lost trampers, hunters and tourists on their mobile phones thanks to a life-saving new technology that provides coverage in dense bush.

Known as Search and Rescue Network, the portable mobile phone coverage will be located in rescue helicopters and will allow anyone lost in New Zealand to talk to rescue crews once the helicopter is in range of their mobile phone.

A prototype of the technology was tested by developers Vodafone, and Police search and rescue in the Hunua Ranges recently.

In its current form, the Search and Rescue Network detects a cell phone 'ping' - a signal mobile phones emit when they are attempting to connect with a nearby cell site.

Once the ping is detected by the equipment inside the helicopter, it shows up on an on-board computer, giving SAR teams a narrowed search area to locate the missing person.

When that person hears the helicopter overhead, they can check for signal bars on their cell phone and make a 111 emergency call, which is answered by rescue crew inside the helicopter.

The missing person can then communicate with the helicopter crew via any mobile phone, providing crucial information such as their condition, any landmarks or other information about their location.

This can then be shared with SAR rescue crews on the ground to help direct their search efforts.

It's hoped the equipment will be used in rescue helicopters around the country within the next 12 months following further enhancements including adding GPS capability and call-bridging so that ground rescue teams can also speak to the lost person.

Vodafone technology director Tony Baird came up with the idea after American tourists Rachel and Carolyn Lloyd were rescued from the Tararua Ranges in May last year.

The mother and daughter had been missing for several days before a rescue helicopter spotted their 'HELP' sign laid out in rocks on the ground.

"I thought 'Oh gosh that's so 20th Century'. We had a helicopter but we didn't know how to find the person and I thought everybody has a cell phone these days, even if you're a visitor from overseas."

Baird said he had used spare parts to create a small version of a cell tower that's transportable in helicopters.

The equipment, which cost about $100,000 to make, still needs to be reduced in weight, from 80kg to about 30kg so as not to take up the space of a person on the helicopter.

Even if a person was unconscious the cell phone would still be transmitting a signal giving rescuers a much more condensed location to search.

The technology won't work if the phone is switched off or the battery is flat but Baird said people should turn off their phones if lost to conserve the battery and switch them back on when they hear a helicopter.

The other option was for hikers and mountain climbers or anyone lost to take a portable phone battery.

"I think it's going to really help save lives. We spend a lot of time and money in New Zealand finding people and the sooner we can find them and save their lives the better.

"It must be quite frightening when you're lost in the middle of nowhere."

Auckland SAR coordinator for police, Sergeant Dene Duthie, said it was exciting to have a two-way communication system in a zero coverage area that let rescuers communicate directly with a missing person.

"There have been a number of cases in the past where technology could have saved us time, money and potentially lives. We are looking forward to this going further," he said.