Problem: Your Polar H7 is paired with the Polar Beat app, but the app keeps giving you an error message that says "Connection to the heart rate sensor was lost"
Solution A: Strap Sensors are Too Dry
Wet the soft strap sensors down MORE than you did when you first put it on (actually run it under water). Buy some electrode gel if water does not work.
Solution B: Hard Reset
Dampen the sensors → Put it on → Unclip the H7 → Remove the battery from the H7 → Clip the H7 back on (to the strap you're still wearing) → Leave it on for ~30 seconds → Unclip the H7 → Reinstall the battery (and cover) → Clip H7 back on → Check to see that it's working
