The stock market is in turmoil, the trade war is dragging on and the global economy is slowing. Plus, it’s been 10 years since the Great Recession ended, making this officially the longest expansion in American history. (Well, probably. More on that in a second.) So perhaps it’s no surprise that forecasters, investors and ordinary people are increasingly asking when the next downturn will arrive.

Economists often say that “expansions don’t die of old age.” That is, recessions are like coin flips — just because you get heads five times in a row doesn’t mean your next flip is more likely to come up tails.

Still, another recession will come eventually. Fortunately, economic expansions, unlike coin-flip streaks, usually provide some hints about when they are nearing their end — if you know where to look. Below is a guide to some of the indicators that have historically done the best job of sounding the alarm.One caveat: Economists are notoriously terrible at forecasting recessions, especially more than a few months in advance. In fact, it’s possible (though unlikely) that a recession has already begun, and we just don’t know it yet.

“Historically, the best that forecasters have been able to do consistently is recognize that we’re in a recession once we’re in one,” said Tara Sinclair , an economist at George Washington University. “The dream of an early warning system is still a dream that we’re working on.”