Scientists have created a wearable sensor that attaches to your underwear and tracks your gut bacteria in real time by measuring the hydrogen gas in your flatulence. And no, that’s not a setup for a joke.

Researchers at the University of Maryland developed the device to solve a problem that has plagued microbiome research for years: how to actually monitor what gut bacteria are doing hour by hour, not just which species are living in there. The answer, it turns out, involves a tiny sensor clipped near your bottom that passively records data while you go about your day.