The difference between an HRM with a chest strap and a device like the MIO is the manner in which they work. Having used both types of technology in the medical field for 20+ years, I can tell you that, while more comfortable, the MIO will give you more problems in dropping beats than a chest strap. The MIO uses a beam of light that measures the distance between it and your radial artery between systole and diastole. Changes in temperature, musculature of the wrist, arterial disease, blood pressure among a few, often cause a difference in readings. The MIO works on the same principal as a pulse oximeter used in a doctor's office or hospital to obtain oxygen saturation and pulse.

An HRM that uses a chest strap works by picking up transthoracic electrical impulses and does not rely on the vascular system or muscle density. As long as a good connection with the skin is maintained, dropping heart beats is less likely to happen. They work on the same principal as an ECG. While a chest strap may be uncomfortable to many, it is more accurate and more reliable.