As Hurricane Harvey dropped anchor over Southeast Texas last week, Zello became the go-to app for rescuers working to save thousands of people trapped by floodwaters.
Within days of Harvey's arrival, the app saw a 20-fold increase in usage in Houston, according to Bill Moore, the Austin based startup's the chief executive.
As Hurricane Irma hurtles across the Caribbean toward the coast of Florida, Zello continues to boom in popularity. The free Internet "walkie-talkie" app - which relies on cellphone data plans or Wi-Fi and is designed to operate in places where signals are weak - became the top app on iTunes and Google Play Wednesday.
The latest influx began Tuesday and, at one point, Moore said, 120 people were registering for the app every second.In recent days, the app has also trended on Facebook and Twitter, offering another example of the pivotal role social media is playing in natural disasters.
Forecasters are calling Irma "a potentially catastrophic Category 5" storm with sustained winds of 185 mph, according to the National Oceanic and Atmospheric Administration. Florida officials have begun evacuating portions of the eastern coastline, which is densely packed with cities, towns and suburbs.
The app has more than 100,000 users worldwide, including in Hong Kong, where it is popular with taxi drivers. The app seems to thrive in locations where government services struggle to meet demand, such as Egypt, South Africa, Venezuela, and parts of the Middle East.
During Harvey, the app allowed victims and rescuers to post voice messages to specific channels, such as "the Cajun Navy" and "Harvey Animal Rescue."
In Houston, volunteers found another way to use the app. By monitoring Facebook, Twitter and Instagram, users were able to feed information to rescue boaters who then took that information and used Zello to coordinate rescues in flooded neighborhoods all over the region.
Source: The Washington Post