I use the wahoo fitness brand chest strap. I like it because it's barebones, clipping on the strap activates it and then it's just a standard bluetooth health d

I use the wahoo fitness brand chest strap. I like it because it's barebones, clipping on the strap activates it and then it's just a standard bluetooth health device that the watch can see and utilise. When paired to the watch, the built-in sensor switches off, which is easy to confirm visually. For comparison: Where the watch's in-built sensor will give me around 12 readings a minute the strap gives me 60 (and this one is around 10 years old now). That's quite useful for HIIT, as well as getting a better judgment for how your heart rate is recovering after brief periods of intensity.