POLAR S610i - Manual (Page 78)

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It is important to be sensitive to your body’s reactions during
the exercise. If you feel unexpected pain or tiredness regarding your
exercise intensity level, it is recommended to stop the exercise or
continue at a lighter intensity.
Notice to persons with pacemakers, defibrillator or other
implanted electronic device. Persons who have a pacemaker use the
Polar heart rate monitor at their own risk. Before starting use, we
always recommend an exercise test under doctor’s supervision. The test
is to ensure the safety and reliability of the simultaneous use of the
pacemaker and the heart rate monitor.
If you are allergic to any substance that comes into contact
with the skin or if you suspect an allergic reaction due to using
the product, check the listed materials in the "Technical
Specifications" chapter. To avoid any skin reaction risk with the
transmitter, wear it over a shirt. However, moisten the shirt well under
the electrodes to ensure flawless operation.
The combined impact of moisture and intense abrasion may cause a
black color, which might stain light-colored clothes especially, to come
off the transmitter's surface.