Patricia Lauder, a 73-year-old Connecticut resident, decided to buy a Fitbit fitness tracker before she retired. Her work kept her at a desk and she wanted to become more active. Gradually she noticed the device showed that her resting heart rate was just getting higher and she was feeling tired all the time.

“When I went to do something, I got even more fatigued, and I wasn’t getting any better,” Lauder recalls. “Every day my heart rate seemed to be jacked up another five points”

Eventually, when her resting heart rate went up to 140, she called an ambulance and went to a cardiologist at UConn Health.

A CT scan revealed that she had two large blood clots in her lungs — pulmonary embolisms — and that her lung artery pressure had spiked to 65, more than twice the norm. Her cardiologist took quick action — clot-busting drugs delivered directly to the lungs through a catheter — which likely headed off a stroke or heart attack.

Within days, she was back to normal and out of the hospital.

“The Fitbit gave them the data they needed,” Lauder says, crediting the device with saving her life.

Although things like the Fitbit are alerting people to problems, they don’t diagnose patients, according to Dr. Gregory M. Marcus, director of clinical research with the Division of Cardiology at the University of California-San Francisco.

But Marcus has launched a study to help scientists learn just how reliable wearable technology can be, in helping to identify common heart problems like atrial fibrillation — a leading cause of, dementia, heart attack, and kidney disease.

“A blood clot can form in the upper chambers of your heart and then move elsewhere,” he said. “Blood thinners can help if you have A-fib, but the problem is that we don’t always know [when] someone has this. How do we identify these people before a stroke?”

Marcus recruited patients with persistent A-fib. Each person was fitted with an Apple Watch and an app called Cardiogram that monitored heart rates. The result – 97 percent of the time the Apple Watch could distinguish between A-fib and a normal heart rhythm.

Brandon Ballinger, co-founder of Cardiogram, says that his app can give the average person a lot of useful information.

“We had a Cardiogram user in his 30s who went out for a run and his pulse went up to 200 [beats per minute],” Ballinger explains. “He had super ventricular tachydaria, the second most common cause of a heart attack.” In another case an Iraq veteran with PTSD was able to look at his Cardiogram app and be reassured, by his heart rate, that he was not having a heart attack during a panic attack.

Cardiogram has now been incorporated into a large study through UCSF called the Health eHeart Study. The study includes 14,000 people and is the largest study using an Apple Watch.

Cardiogram delivers other useful information for consumers. It can help people understand when they are getting the most restful sleep.

Another bit of useful information is your resting heart rate recovery rate. Two minutes after you finish exercising, your heart rate should be heading back to whatever normal is for you.

Another significant measurement that comes from Cardiogram is stress levels. Spikes in heart rate, observed through Apple Watches, seem to be most commonly related to stress. Being aware of this and using deep breathing, exercise or meditation, can help resolve the issue.

Wearable devices can also help people discover problems like sleep apnea and diabetes, in addition to abnormal heart rhythms.

“It’s fun to be working at the intersection of artificial intelligence, medicine and mobile design,” Ballinger says.

Adds Marcus: “There is great promise in this. Devices have largely been used to enhance health under the general category of fitness but they haven’t yet become accurate for diagnoses. We need to leverage this amazing technology to go towards implementing health care.”

A growing number of wearable fitness and health monitors have entered the market in the past five years. Which one is right for you? Here’s a primer.

• Fitbit, one of the most popular devices, can tell you how many steps you have taken, distance covered, your heart rate, and, if you wear it at night, your sleep patterns.
• PIP devices, used with a smart phone app, provide immediate feedback about your stress levels. New Doppel devices can deliver a heartbeat-like vibration onto the inside of your wrist.
• Withings monitors, which work with an app through Bluetooth, can take blood pressure readings and report averages to your doctor.
• AliveCor is a mobile phone-based electrocardiogram. It is tiny and attaches to your phone case.
• Viatom Checkme measures your body temperature, as well as your pulse rate and heart rhythm, oxygen saturation, systolic blood pressure, physical activity, and sleep quality.
• Muse makes a headband that works as a brain-sensing device that gives you feedback about your meditation practice. It doesn’t change your brain but helps you to change for better meditation practice.
• Gymwatch Fitness Tracker is a device worn on the arm or leg that helps you you build muscle properly. Consider it your own fitness coach.

In addition, a number of fitness apps have been developed for iPhone and Android that can track your diet, exercise, physical symptoms, and sleep. They can also be used as reference tools to look up medications or conditions.