<P> Strapless heart rate monitors (often referred to as "wearables") now allow the user to just touch two sensors on a smartwatch display for a few seconds to view heart rate data . These are popular for comfort and ease of use, though they don't give as much detail as monitors that use a chest strap . Some models of these variations of heart rate monitors use either infrared light or red visible light to measure the heart rate, as opposed to two or more electrodes . In addition to measuring the heart rate, devices using this technology are able to measure blood oxygen saturation (SpO) </P> <P> More advanced models offer measurements of heart rate variability, activity, and breathing rate to assess parameters relating to a subject's fitness . Sensor fusion algorithms allow these monitors to detect core temperature and dehydration . </P> <P> Another style of heart rate monitor replaces the plastic around - the - chest strap with fabric sensors - the most common of these is a sports bra that includes sensors in the fabric . </P> <P> In old versions, when a heart beat is detected a radio signal is transmitted, which the receiver uses to determine the current heart rate . This signal can be a simple radio pulse or a unique coded signal from the chest strap (such as Bluetooth, ANT, or other low - power radio link); the latter prevents one user's receiver from using signals from other nearby transmitters (known as cross-talk interference). </P>

Machine that measures heart rate in the hospital