Some customers have asked the correct way to put on and wear the Heart Rate Monitor (HRM)
The HRM should come with two band sizes, big and small.
Figure out which band size works best for your child, and then when putting it on, make sure that the blinking lights at the bottom of the sensor have direct contact with the skin. The sensor should be snug, but doesn't have to be tight. It shouldn't move around much when moving your arm. Some kids have to put it around their bicep or leg, which is also fine - as long as there is direct contact.
Here are some example pictures of how to wear it: