Walkie-talkie app Zello becomes No. 1 in anticipation of Hurricane Irma

Hurricane Harvey rescuers turned to walkie-talkie app Zello while working to save thousands trapped by floodwaters last week.

As Hurricane Irma runs through the Caribbean and approaches Florida, downloads of the app have surged, making it the top app in iTunes and Google Play.

Zello is a free walkie-talkie app that can be used on smartphones, tablets or PCs. The app uses cells data service or Wi-Fi to make your device into a two-way radio. It requires less bandwidth than a phone call, meaning the walkie-talkie will often work when calls won't go through.

Hoping to dispel misinformation, Zello has warned that internet service, either through Wi-Fi or cellular data, is necessary to use the app.

Zello has also warned that the app uses a lot of battery power. It is recommended to have an external battery or power source. If your phone has low battery, Zello recommends turning off the app and enabling push notifications when it is not in use.

During Harvey rescue efforts, groups like the Louisiana Cajun Navy instructed those needing help after Hurricane Harvey to download the app saying, "The best source of communication at this time is the Zello walkie-talkie app."