CBS Local — An app that allows users to instantly trade voice messages and photos is becoming the must-have survival item for many Americans preparing for Hurricane Irma.

The Zello Walkie Talkie has reportedly jumped to the top of the Apple store’s free app chart as people look for ways of staying in touch with their friends and loved ones when the Category 5 storm arrives. Zello was created in 2011 and has reportedly been used by rescue workers called the Cajun Navy following Hurricane Katrina.

Since Hurricane Harvey made landfall in Texas, new channels have been created on the app for groups doing search and rescue missions around the flood-ravaged Houston area.¬†“Our voice is how we most naturally communicate. A few seconds of voice has so much information on emotion, education, gender, what part of the country are they from,”¬†said Zello CEO Bill Moore.

Zello had around 100 million registered users on iOS and Android at the beginning of 2017. Some of the new users downloaded the app under the false belief it could function without a WiFi signal. Rumors of the app’s ability to work connection-free have since been knocked down by Zello and multiple consumer reports.

Florida residents have already been urged to prepare for or evacuate the state as Irma in expected to bring winds of over 180 mph to the region.