Michael Snyder, professor and chair of genetics at the Stanford University School of Medicine sports wearable gadgets. Wearable gadgets gave a Snyder an early warning that he was getting sick before he ever felt any symptoms of Lyme disease.

WASHINGTON — A next step for smart watches and fitness trackers? Wearable gadgets gave a Stanford University professor an early warning that he was getting sick before he ever felt any symptoms of Lyme disease.

Geneticist Michael Snyder never had Lyme’s characteristic bull’s-eye rash. But a smart watch and other sensors charted changes in Snyder’s heart rate and oxygen levels during a family vacation. Eventually a fever struck that led to his diagnosis.

Say “wearables,” and step-counting fitness trackers spring to mind. It’s not clear if they really make a difference in users’ health. Now Snyder’s team at Stanford is starting to find out, tracking the everyday lives of several dozen volunteers wearing devices that monitor more than mere activity.

He envisions one day having wearables that act as a sort of “check engine” light indicating it’s time to see the doctor.

“One way to look at this is, these are the equivalent of oral thermometers but you’re measuring yourself all the time,” said Snyder, senior author of a report released Thursday on the project.

Among the earliest hints: Changes in people’s day-to-day physiology may flag when certain ailments are brewing, from colds to Lyme to Type 2 diabetes, researchers reported in the journal PLOS Biology.

Interest in wearable sensors is growing along with efforts to personalize medicine, as scientists learn how to tailor treatments and preventive care to people’s genes, environment and lifestyle. The sensors are expected to be a part of the National Institutes of Health’s huge “precision medicine” study, planned to begin later this year.

But a first step is learning what’s normal for different people under different conditions.

The Stanford team is collecting reams of data — as many as 250,000 daily measurements — from volunteers who wear up to eight activity monitors or other sensors of varying sizes that measure heart rate, blood oxygen, skin temperature, sleep, calories expended, exercise and even exposure to radiation. That’s paired with occasional laboratory tests to measure blood chemistry and some genetic information.