With the Category 5 Hurricane Irma, now one of the strongest hurricanes ever recorded in the Atlantic, on its way toward the Caribbean and possibly the southeastern tip of the US, a little-known walkie-talkie app has shot to the top of Apple’s App Store. The free app, called Zello Walkie Talkie, lets your phone communicate as a two-way radio so long as you have a network or Wi-Fi connection. What makes it useful is that it allows immediate voice communication to others in a shared channel, as opposed to having to place a phone call and hope someone on the other end picks up. The ad-free service can also be used to send texts and photos.

Zello first began rising in the top free chart as Tropical Storm Harvey made landfall in Texas as a Category 4 hurricane two weeks ago. According to USA Today, the app is the go-to service for rescue workers in the Houston area. Zello CEO Bill Moore told the paper that its service saw 20 times as many new users in Houston last week as rescue efforts ramped up.

The app’s usage is only going to increase as preparations for Irma continue and residents in the Caribbean and Florida prepare for the worst. The company’s official Facebook page says Zello Walkie Talkie is seeing as many as 7,000 new registrations per minute, and the team is working tirelessly to maintain uptime as usage skyrockets. The National Hurricane Center predicts Irma may hit southern Florida as early as this weekend.

Correction: An earlier version of this article incorrectly identified the name of an island Hurricane Irma had passed over in a satellite image posted above. It is Barbuda, not Bermuda.