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-Reads from TIME
- Caitlin Clark Is TIME's 2024 Athlete of the Year
- Where Trump 2.0 Will Differ From 1.0
- Is Intermittent Fasting Good or Bad for You?
- The 100 Must-Read Books of 2024
- Column: If Optimism Feels Ridiculous Now, Try Hope
- The Future of Climate Action Is Trade Policy
- FX’s Say Nothing Is the Must-Watch Political Thriller of 2024
- Merle Bombardieri Is Helping People Make the Baby Decision
Contact us at letters@time.com