A lot of fitness trackers come bundled with a chest strap, to get the most accurate heart rate readings. (heavy.com)
It was heavy, clunky, and rumours of having to wear it palm side up to get accurate heart rate readings were right. (itwire.com)
As I said in my Fitbit Charge HR review, you'll still want to pick up a chest strap if you're looking for more accurate heart rate readings. (androidauthority.com)