Polar Cardiaca 0H1 Optic Frequency Sensor

With internal memory you can only train with OH1 and then transfer your training data to your smartphone. Includes a washable arm band in the washing machine.

To accurately measure the heart rate it is necessary to wear the OH1 comfortably on the forearm or arm. The sensor must always be in contact with the skin, but the arm band should not be too tight to prevent it from blocking blood flow.  For a more precise heart rate measurement, it is recommended to wear the OH1 for a few minutes before starting the heart rate measurement.