‘Seismic alert!’: Apps warn Mexicans of quakes

Early warning system: SkyAlert founder Alejandro Cantu says his app's sensors send a broadband signal to phones, triggering a loud sound with a voice that repeats

MEXICO CITY: A powerful earthquake strikes off the Pacific coast of Mexico. Within seconds, radio transmissions, megaphones and smartphone apps blare warnings to the capital’s 20 million people before the ground shakes. 

After the loud “seismic alert!” alarm, Mexico City residents have as much as a minute to flee their homes, offices and schools before buildings start to sway.