The GoodSAM app is being rolled out across the country which alerts bystanders to cardiac arrests near them.

If saving a life is on your to-do list, a new smartphone app is here to help.

The new technology, named GoodSAM, aims to increase a person's chances of surviving a cardiac arrest by alerting CPR-trained members of the public to emergencies nearby.

Based on an ancient parable about human decency and an old myth that you are never more than three feet away from a spider, the app will be launched nationwide this weekend.

ROBERT KITCHIN/STUFF Wellington Free Ambulance has adopted the GoodSam app, which alerts bystanders to people suffering cardiac arrests nearby.

GoodSAM, which stands for good smartphone activated medics, uses GPS to alert the nearest three bystanders to someone having a cardiac arrest, in the hope they might be able to provide help until an ambulance arrives.

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They could be off-duty doctors, medics on holiday, or anyone who happens to be trained in CPR.

ROBERT KITCHIN/STUFF Wellington Free Ambulance relationship and development manager Vanessa Simpson shows off the GoodSam app.

It also lets them know where the nearest defibrillators are.

Wellington Free Ambulance medical director Dr Andy Swain said the chance of surviving a cardiac arrest in New Zealand is about 15 per cent.

"For every minute without CPR or defibrillation, survival decreases by 10 per cent."

ROBERT KITCHIN/STUFF Emergency medical dispatcher Brenda Slieker in the Ambulance Communications Centre in Wellington. Through the GoodSAM app, dispatchers can trigger an alert on GoodSAM at the same time they send an ambulance to a cardiac arrest.

The Wellington service aims to get ambulances to people within six minutes of a call, but that's not always possible, WFA paramedic Vanessa Simpson said.

Survival is largely due to the quick actions of bystanders initiating help within the first few minutes.

St John medical director Dr Tony Smith said alerting community "responders" to people nearby who are in cardiac arrest can amplify the call for help.

"Imagine you are at home, a mall or other public space, and someone in the vicinity suffered a cardiac arrest. You were able to respond and help, but you just needed to be alerted," he said.

"Wouldn't you want to know?"

There was a chance that push alerts and location accuracy could be difficult in places with poor 2G or 3G network coverage, but these people can register to receive alerts by text message.

People can also log on to a computer and tell GoodSAM where they are.

Trained frontline personnel within St John and Wellington Free Ambulance have been using the free app since December.

Staff have responded to 78 calls in that time, including when they were on holiday.

It has increased the chances of surviving a cardiac arrest in Wellington by 14 per cent, Simpson said.

For people who want to learn CPR, Wellington Free Ambulance runs free "Heartbeat" courses, which serve as introductions or refreshers to using defibrillators and CPR.

The GoodSAM app was developed years ago in London, and has been implemented by several ambulance services around the world, including the United Kingdom.

"The more people who download the app, the more coverage we will achieve across New Zealand, and the more likely we are to improve outcomes from cardiac arrest," Smith said.

The app was part-funded through a $35,000 donation by The Gift Trust.

Rollout in New Zealand is supported by the New Zealand National Cardiac Network and the New Zealand Resuscitation Council.

The app is free for Apple and Android.

HOW IT WORKS

* The GoodSAM app lets anyone – patients, bystanders or emergency personnel – trigger an alert.

* It asks if 111 has been called and says it can place a call if needed.

* GoodSAM then uses GPS to alert the nearest three people that someone needs help. It also lets them know where defibrillators are.

* There is no obligation to accept the call. If all three people hit "reject" then the alert drops.

* Anyone with first aid training can get the app. Credentials must be uploaded to the site.

* To register and download the app go to: stjohn.org.nz/goodsam.