Why does the display of my Polar training device fog up?
Don’t worry if the display of your Polar training device fogs up. It’s a temporary phenomenon and completely normal if there’s a sudden change of temperature; it might occur, for example, if you wear your device indoors, where it’s humid and warm, and then go out to start your training in cooler conditions. It’s not harmful to your training device, and the fog in the display should dry out shortly.
However, if the display of your training device stays foggy for longer, the water resistance of your Polar device should be checked by an authorized Polar Service Center. See this page for more info.