I used the Pro 3s as a heart rate sensor yesterday. The iPhone Fitness app has a “Indoor Run” workout. With iOS 26.x and Pro 3 pods, the app uses the heart rate sensors and some other accelerometer data to calculate distance and calories burned. It also displays current heart rate.
Unless you have it linked to an Apple watch, there isn’t a way to calibrate, though.
I don’t know the accuracy of the treadmill distance measurement, so I really don’t know the accuracy of the pods. I went 3.22 miles on the treadmill and the app showed 2.9 miles, about a 10% difference. The calories burned calculation on the treadmill showed 420 and the app showed 349. I don’t know where the app got things like age, height, and weight that it uses for calculating distance and calories.
My treadmill was programmed for a 5 minute warmup, 30 minute run alternating between faster speed and no slope, and slower speed with higher slope. Then a 5 minute cooldown. Total distance was 3.22 in 40 minutes.
The next time I do a long walk I will try to remember to start that app.
The Pro 3 has some fun features.
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