The U.S. Food and Drug Administration (FDA) on Tuesday authorized the first wearable sensor that continuously tracks ketones—chemicals the body makes when it burns fat instead of sugar for fuel.

It is also the first device anywhere to monitor ketones and blood sugar at the same time, the FDA said.

When ketones climb too high, they can cause diabetic ketoacidosis, or DKA. The American Diabetes Association warns that DKA can worsen within hours and lead to coma or death if it goes untreated.