Review on Polar H10 Bluetooth Heart Rate Monitor, Compatible with iPhone & Android - Black Chest Strap HRM by Ada Kuakowska ᠌

Pros: It immediately pairs with the Apple Watch, which solves a separate problem of buying expensive sports watches with a chest pulse sensor for running. Great for beginner runners. Change the battery every 3-6 months, depending on the number of workouts and their duration. Cons below: It is not clear when the heart readings are read from the polar sensor, and when from the watch sensor. Once (for half a year) the polar sensor itself turned off and when draining the training data, I only noticed that the data came from the watch sensor (on the graph you can see it in any tracker) and not from the polar.