Went for a walk today, turned on "exercise" mode.. it kept the HRM on the whole time..once recording it at 63.. my heart rate isn't that low when I'm asleep, let alone walking at 3 mph. It got more accurate as I went and seems it might be able to replace my Polar -- the cals burned needs to be accurate and I will check that at the gym this week. Make sure it's snug enough.