The “Yo” app was developed as a joke. Download the app, tap on a friend’s name, and they’d get a message from you saying “Yo.” It’s that simple. In fact, the app was created in eight hours and released on April Fools’ day just so people would know it was a gag.
But Yo has a new application that’s no laughing matter. Developers in the Middle East are using the app to warn Israelis of possible attacks from rocket fire; users following the handle “RedAlertIsrael” will get a “Yo” at the same time the country’s sirens go off.
One person’s gag app is apparently another’s survival tool.
More Must-Read Stories From TIME
- Supreme Court Overturns Roe v. Wade, Undoing Constitutional Right to Abortion
- What the Supreme Court’s Abortion Decision Means for Your State
- The Failure of the Feminist Industrial Complex
- The Fight Over Abortion Has Only Just Begun
- Column: How Stereotypes Shape the Language People Use
- Everything We Know About Beyoncé's New Album, Renaissance
- Homes Made from Straw or Fungi Can Now Get You a Cheaper Mortgage in the Netherlands
- Going on Vacation This Summer? Welcome to the 'Revenge Travel' Economy
Read More From TIME