The Apple Watch Series 4 also has F.D.A. clearance for both its irregular heart rhythm alert and its ECG, which operates with an electrical heart sensor. Users take an ECG by placing a finger on the digital crown for 30 seconds. Electrodes in the crown and in the back crystal work in concert. Afterward, a user can add symptoms and generate a PDF. But there’s no option to automatically send the result to a doctor.

Dr. Frisch said the quality of recordings from the Kardia and the latest Apple Watch were very similar and provide a single view of the heart that is “an approximation” of the standard EKG. But Kardia is coming out with a new device, the KardiaMobile 6L, which Dr. Frisch said would allow doctors to view the same heart rhythm from six different angles. Users rest the 6L on the bare skin of either their left knee or their ankle and hold it in place with two fingers for 30 seconds.

Diabetics, too, have new devices that can help them monitor their blood sugar.

“The most painful part of diabetes is the finger stick,” said Kathleen Weaver, 59, of Dallas, a dog owner and handler who trains beagles and travels frequently for competitions. She said she used to have to test her blood up to 10 times a day. Now she wears a Dexcom G6 continuous glucose monitor, which doesn’t require drawing blood.

Its sensor remains attached to the skin on her abdomen for up to 10 days, and she also uses an insulin pump. The Dexcom transmits glucose readings every five minutes, and connects wirelessly to a reader device or via an app to her smartphone and smartwatch and sends her alarms when her blood sugar goes high or low.

She said the biggest advantage of the Dexcom was not having to “let blood every time you need to go check the numbers, and then it does check the numbers a lot more often.”

Since her medical devices are hidden beneath her clothing, Ms. Weaver said, she can be discreet when she wants to know her number. “I can say, ‘Hey, Siri, what’s my blood sugar?’”