Stopwatch

Watches are generally very useful. The watches installed on people's wrists these days can tell three things: how long until they meet their soulmate, how long until their next life changing moment occurs, and how long until they die. Some like to cover their watches. Some like to know. But when everyone's watch vibrates at the same time, the world looks at their watches to see another timer has appeared.
End on the world: 3 days, 0 hours, 0 minutes, 0 seconds.