Worldwide, two in three deaths - 35 million each year - are unregistered. Around 180 countries that are home to 80 percent of the world's population do not collect reliable cause of death statistics, researchers said.
A team led by researchers at the University of Melbourne and the University of Washington redesigned a short 'verbal autopsy' questionnaire and tested it in India, the Philippines, Mexico, and Tanzania.
The app was then field-tested in China, Sri Lanka and Papua New Guinea.
Family members of the deceased were given surveys in hand-held devices. A computer then analysed the data to make a diagnosis, bypassing the need to rely on doctors to do this work.
The research was published in the journal BMC Medicine.