Do your research before you purchase one. While they are certainly more comfortable than a chest strap, there are many published reports about their accuracy. Unlike the chest straps that use transthoracic conductivity (as does an EKG) to detect a heart rate, the optical sensors use capillary refill time (as does a pulse oxcimeter) to detect a pulse rate. There are too many variables that can cause inaccurate capillary refill detection during exercise.