Similar to the other commenter, I also wear my HR chest strap so that it sits under the bottom band of my bra. The bra seems to keep it in place, and when I’ve tried it lower it always feels on the verge of slipping down to my waist. It’s not the most comfortable thing ever and takes some adjusting to find a fit that’s not too tight/loose. That said, I know it’s much more accurate than the optical HR on my watch so I just live with it. I’ve worn the same one for a few years and don’t notice it anymore but it still feels nice to take off after workouts 🙂