No one knows better than the Japanese what a difference a few minutes — or even seconds — warning can mean when a major earthquake or tsunami is on its way. That’s why they have developed the world’s most sophisticated early warning system.

9to5Mac reports that the latest beta of iOS 5 — the new mobile operating system Apple (AAPL) is scheduled to deliver this fall — includes a toggle switch on Japanese iPhones that, when flipped on, will alert users whenever it’s time to take shelter.

GigaOm‘s Darrell Etherington points out that Japanese feature phones have been offering access to the same early warning service for several years. But he suggests that its appearance in iOS 5 beta may signal an initiative on Apple’s part to provide localized warning services in other parts of the world. Mexico has a similar earthquake warning system, for example, and California is working on one that’s expected to come online in 2013. Meanwhile, now that the iPhone’s creaky notification system has finally been rewritten, perhaps Apple will start offering different kinds of built-in alerts — wildfires in the American West, floods in the East, tornadoes in the MidWest, etc.