"Our goal is to create an app that will turn a mobile phone into a personal 'emergency beacon'," said Tanya O'Carroll, Amnesty International's Technology and Human Rights Project Officer.
"It will enable activists at risk of being seized, detained – or ‘disappeared’ by their own governments – to get out that vital first alert to those who can act to protect them."
Panic Button works by allowing individuals at risk to broadcast their location to a pre-determined list of contacts, with updates on their whereabouts sent every five minutes after the app is activated.
For their security, this never shows in the phone outbox and the app runs invisibly in the phone's background.
Amnesty International worked with developers from global IT company Thoughtworks to prototype the app on Android.
It was tested in Nairobi with human rights activists from around the world, who considered it a vital security tool for individuals at risk - especially women.
“Women often face violence and if they were provided with this tool it could be a saviour for them,” said one Ugandan woman human rights activist.
A Pakistani activist added: “For human rights defenders, and especially for women in the conflict zones, the situation could be better if they had access to such technology."
Amnesty International developed the app over the past year in an open design process involving more than 650 designers, developers, human rights activists and NGOs.
The original idea belonged to Amy Bonsall, who submitted it in an open innovation challenge run by global design consultancy OpenIDEO in November 2011. A team of volunteers then created the first prototype over a single weekend at IDEO in London.
The Global Impact Awards support organizations using technology to help transform lives.
Along with a £500,000 grant, the top four submissions will also receive Google mentoring to help make their project a reality.
Voting opens today and closes on 31 May, and the four winners will be revealed by the judges on 3 June.
“The web's contribution to economic progress has been much celebrated, but I believe that we are only scratching the surface of its potential to solve social and political problems," said judge Berners-Lee.