MyShake, available on Android phones, links users to become an all-in-one earthquake warning system; it records quake-type rumblings, ties a critical number of users to a location, and could eventually provide a countdown to the start of shaking.
Its inventors say the app, released by the University of California, Berkeley, could give early warning of a quake.
"MyShake cannot replace traditional seismic networks," said Richard Allen, leader of the app project. "But we think MyShake can make earthquake early warning faster and more accurate in areas that have a traditional seismic network, and can provide life-saving early warning in countries that have no seismic network."
The software behind MyShake, developed by a handful of Silicon Valley programmers, relies on the same technology smartphone gamers depend on to sense the phone's orientation, known as the accelerometer, in order to measure movement caused by quakes.
What smartphones lack in sensitivity - they can only record earthquakes above magnitude 5 within 10 kilometres - they make up for in ubiquity.
Currently, 300 smartphones equipped with MyShake within a 110-km square area are enough to estimate a quake's location, magnitude and origin time.
There were some 3.4 billion smartphone subscriptions worldwide in 2015, according to the Ericsson Mobility Report, so the app's creators hope to build a seismic network covering the globe.
"We want to make this a killer app, where you put it on your phone and allow us to use your accelerometer, and we will deliver earthquake early warning," Allen said.
Sophisticated early-warning systems can warn of coming quakes as much as a few minutes before they begin, but cannot stop them causing death and destruction on a large scale.