Smartwatches keep tabs on health, still track fitness

Electrocardiograms measure the timing and strength of the electrical pulses that keep your heart pumping. On the Apple Watch, the ECG kicks into action when you launch the app and hold your

finger against the digital crown, the home button on the upper right side of the watch, for 30 seconds. Electrodes are built into the back crystal and digital crown of the watch. If you

receive a “sinus rhythm” result, it means the watch has detected a normal heartbeat, not A-fib. Regardless of the result, you’re urged to seek medical attention if you experience any

symptoms. Apple makes it clear that its watch does not check for signs of a heart attack. Fitbit’s irregular heart rhythm notifications about possible A-fib work across several models and

are powered by Fitbit’s photoplethysmography (PPG) algorithm, which passively assesses your heart rhythm in the background while you’re still or sleeping. 2. SKIN SENSOR. Fitbit added an

electrodermal (EDA) sensor to its Fitbit Sense watch and its successor, Fitbit Sense2. When you place your palm over the face of the device, sensors can detect subtle electrical changes in

the sweat level of your skin. Factored with your heart rate, sleep and activity data, Fitbit calculates a stress management score of 1 to 100, with a higher number translating to fewer 

physical signs of stress and a lower number meaning more signs. Similar sensors on Pixel Watch 2 can also detect stress. Fitbit may recommend breathing exercises and other mindfulness tools

to help you manage stress. But after a free trial period, you’ll have to sign up for a premium subscription service for a deeper dive into the metrics. The subscription costs $9.99 monthly

or $79.99 annually. Another sensor on the Fitbit Sense can detect variations in skin temperature. Apple added wrist temperature sensors to the Series 8 and later watches, including the more

rugged $799 Apple Watch Ultra. For its part, Samsung added an infrared temperature sensor on Galaxy Watch5 and later smartwatches. Getty Images 3. SLEEP TRACKING. Some devices, including

high-end Fitbits and Galaxy smartwatches, track the quality of your slumber time right down to various sleep stages and the number of times you wake up in the middle of the night. Apple’s

watch is more about setting up the conditions so you get a good night’s sleep, starting with a wind-down routine before bedtime. But it, too, has the ability to detect sleep stages. Of

course, if you’re planning to sleep with any of the smartwatches, make sure they are charged before you go to bed, and if needed, give them some extra juice when you wake up. 4. BLOOD

OXYGEN. Fitbit/Google, Garmin, Mobvoi and Samsung all have models that can measure blood oxygen levels. The Apple Watch Series 6, Series 7 and Series 8 obtain a measurement from a quartet of

clusters of green, red and infrared LEDs on its rear and four photodiodes spaced and isolated between them to determine the color of your blood. Measurements are automatically collected

throughout the day or when you’re asleep. You also can launch an app to take a manual reading by steadying your wrist on a table, with the watch display facing upward, tapping Start, and

then waiting patiently while a timer counts down for 15 seconds. But Apple removed the blood oxygen feature on its Series 9 and Ultra devices following a patent infringement dispute with an

Irvine, California, company called Masimo. The watches are now for sale in the U.S. without the feature. Masimo’s own $499 FDA-cleared W1 Medical watch includes real-time monitoring of a

users’ oxygen saturation and pulse rate and is expected to be out this year. While most healthy adults report blood oxygen levels between 95 percent and 100 percent, what does a lower

reading signify? Blood oxygen is an indicator of early signs of circulatory, heart or lung function issues, such as anemia, neurological problems or sleep disorders, says Leslie Saxon, M.D.,

a professor of medicine and executive director at the Center for Body Computing at the University of Southern California.