Google's smartphone earthquake detection system, currently being trialled in New Zealand, was triggered for the first time by yesterday's 3.4 magnitude quake in Christchurch.
The tech giant announced last month that Aotearoa and Greece would be trialling the system, which was previously only available in parts of the US.
The earthquake, centred just east of the city, hit at 11.49am yesterday. Android-based phones detected seismic waves using their built-in accelerometers and sent a signal, including rough location, to a central server.
The server then used other phones to figure out if an earthquake was actually happening, where it was and its magnitude.
The system is unrelated to New Zealand's National Emergency Management Agency system, which has alerted Kiwis to previous earthquakes as well as COVID-19 lockdowns.
Android users who do not wish to receive the automated alerts can turn it off in device settings. There is currently no comparable system for Apple's iPhone users.
"Users will receive automatic early warning alerts when there is an earthquake in their area," wrote Boone Spooner, an Android Product Manager, in a company blog post at the time the trial was announced.
"Through this system, we hope to provide people with the advance notice they need to stay safe."
And that proved to be the case, with one Cashmere resident, Miranda, telling Stuff she received an alert shortly before she felt the quake.
"It actually worked. I was using my phone when the alert came in. I'd just read the words 'earthquake safety info' before the ground moved. It's pretty cool," she said.
The Android alert estimated the magnitude of the quake at 4.6, above Geonet's 3.4 categorisation. But as an early warning tool, it did what it was supposed to, Miranda continued.
"It takes away that first thought that it's just a bus or a truck going past," she told Stuff.
"It would give you a chance to get away from that bookcase or something near you that could fall."